diff --git a/.baseline/checkstyle/checkstyle.xml b/.baseline/checkstyle/checkstyle.xml
index 836253558cef0..b327ab7a6c7fc 100644
--- a/.baseline/checkstyle/checkstyle.xml
+++ b/.baseline/checkstyle/checkstyle.xml
@@ -1,7 +1,7 @@
 <?xml version="1.0"?>
 <!DOCTYPE module PUBLIC
-        "-//Puppy Crawl//DTD Check Configuration 1.3//EN"
-        "http://www.puppycrawl.com/dtds/configuration_1_3.dtd">
+        "-//Checkstyle//DTD Checkstyle Configuration 1.3//EN"
+        "https://checkstyle.org/dtds/configuration_1_3.dtd">
 
 <!--
     Palantir Baseline Checkstyle configuration.
diff --git a/assembly/pom.xml b/assembly/pom.xml
index 8ff32b0f5a39a..f7bfb279e7dc8 100644
--- a/assembly/pom.xml
+++ b/assembly/pom.xml
@@ -20,12 +20,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-assembly_2.12</artifactId>
+  <artifactId>spark-assembly_2.11</artifactId>
   <name>Spark Project Assembly</name>
   <url>http://spark.apache.org/</url>
   <packaging>pom</packaging>
diff --git a/common/kvstore/pom.xml b/common/kvstore/pom.xml
index f042a12fda3d2..23a0f49206909 100644
--- a/common/kvstore/pom.xml
+++ b/common/kvstore/pom.xml
@@ -21,12 +21,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-kvstore_2.12</artifactId>
+  <artifactId>spark-kvstore_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project Local DB</name>
   <url>http://spark.apache.org/</url>
diff --git a/common/network-common/pom.xml b/common/network-common/pom.xml
index 56d01fa0e8b3d..41fcbf0589499 100644
--- a/common/network-common/pom.xml
+++ b/common/network-common/pom.xml
@@ -21,12 +21,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-network-common_2.12</artifactId>
+  <artifactId>spark-network-common_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project Networking</name>
   <url>http://spark.apache.org/</url>
diff --git a/common/network-shuffle/pom.xml b/common/network-shuffle/pom.xml
index a6d99813a8501..ff717057bb25d 100644
--- a/common/network-shuffle/pom.xml
+++ b/common/network-shuffle/pom.xml
@@ -21,12 +21,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-network-shuffle_2.12</artifactId>
+  <artifactId>spark-network-shuffle_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project Shuffle Streaming Service</name>
   <url>http://spark.apache.org/</url>
diff --git a/common/network-yarn/pom.xml b/common/network-yarn/pom.xml
index 55cdc3140aa08..a1cf761d12d8b 100644
--- a/common/network-yarn/pom.xml
+++ b/common/network-yarn/pom.xml
@@ -21,12 +21,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-network-yarn_2.12</artifactId>
+  <artifactId>spark-network-yarn_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project YARN Shuffle Service</name>
   <url>http://spark.apache.org/</url>
diff --git a/common/sketch/pom.xml b/common/sketch/pom.xml
index 3c3c0d2d96a1c..adbbcb1cb3040 100644
--- a/common/sketch/pom.xml
+++ b/common/sketch/pom.xml
@@ -21,12 +21,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-sketch_2.12</artifactId>
+  <artifactId>spark-sketch_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project Sketch</name>
   <url>http://spark.apache.org/</url>
diff --git a/common/tags/pom.xml b/common/tags/pom.xml
index 883b73a69c9de..f6627beabe84b 100644
--- a/common/tags/pom.xml
+++ b/common/tags/pom.xml
@@ -21,12 +21,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-tags_2.12</artifactId>
+  <artifactId>spark-tags_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project Tags</name>
   <url>http://spark.apache.org/</url>
diff --git a/common/unsafe/pom.xml b/common/unsafe/pom.xml
index 93a4f67fd23f2..62a2ba4d684b9 100644
--- a/common/unsafe/pom.xml
+++ b/common/unsafe/pom.xml
@@ -21,12 +21,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-unsafe_2.12</artifactId>
+  <artifactId>spark-unsafe_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project Unsafe</name>
   <url>http://spark.apache.org/</url>
diff --git a/core/pom.xml b/core/pom.xml
index c374862a5d64e..1e9f428d86860 100644
--- a/core/pom.xml
+++ b/core/pom.xml
@@ -20,12 +20,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-core_2.12</artifactId>
+  <artifactId>spark-core_2.11</artifactId>
   <properties>
     <sbt.project.name>core</sbt.project.name>
   </properties>
diff --git a/dev/checkstyle.xml b/dev/checkstyle.xml
index e8859c01f2bd8..78f647a70f2e3 100644
--- a/dev/checkstyle.xml
+++ b/dev/checkstyle.xml
@@ -16,8 +16,8 @@
   -->
 
 <!DOCTYPE module PUBLIC
-          "-//Puppy Crawl//DTD Check Configuration 1.3//EN"
-          "http://www.puppycrawl.com/dtds/configuration_1_3.dtd">
+        "-//Checkstyle//DTD Checkstyle Configuration 1.3//EN"
+        "https://checkstyle.org/dtds/configuration_1_3.dtd">
 
 <!--
 
diff --git a/dev/deps/spark-deps-hadoop-palantir b/dev/deps/spark-deps-hadoop-palantir
index 9ff692d690ddb..84c46f1aa5a61 100644
--- a/dev/deps/spark-deps-hadoop-palantir
+++ b/dev/deps/spark-deps-hadoop-palantir
@@ -22,10 +22,10 @@ aws-java-sdk-bundle-1.11.201.jar
 azure-data-lake-store-sdk-2.2.3.jar
 azure-keyvault-core-0.8.0.jar
 azure-storage-5.4.0.jar
-breeze-macros_2.12-0.13.2.jar
-breeze_2.12-0.13.2.jar
+breeze-macros_2.11-0.13.2.jar
+breeze_2.11-0.13.2.jar
 chill-java-0.9.3.jar
-chill_2.12-0.9.3.jar
+chill_2.11-0.9.3.jar
 classmate-1.1.0.jar
 commons-beanutils-1.9.3.jar
 commons-beanutils-core-1.8.0.jar
@@ -107,7 +107,7 @@ jackson-mapper-asl-1.9.13.jar
 jackson-module-afterburner-2.9.7.jar
 jackson-module-jaxb-annotations-2.9.7.jar
 jackson-module-paranamer-2.9.7.jar
-jackson-module-scala_2.12-2.9.7.jar
+jackson-module-scala_2.11-2.9.7.jar
 jackson-xc-1.9.13.jar
 janino-3.0.10.jar
 javassist-3.20.0-GA.jar
@@ -134,10 +134,10 @@ jetty-util-6.1.26.jar
 jetty-util-9.4.12.v20180830.jar
 joda-time-2.10.jar
 json-smart-1.3.1.jar
-json4s-ast_2.12-3.5.3.jar
-json4s-core_2.12-3.5.3.jar
-json4s-jackson_2.12-3.5.3.jar
-json4s-scalap_2.12-3.5.3.jar
+json4s-ast_2.11-3.5.3.jar
+json4s-core_2.11-3.5.3.jar
+json4s-jackson_2.11-3.5.3.jar
+json4s-scalap_2.11-3.5.3.jar
 jsp-api-2.1.jar
 jsr305-3.0.2.jar
 jtransforms-2.4.0.jar
@@ -150,8 +150,8 @@ leveldbjni-all-1.8.jar
 log4j-1.2.17.jar
 logging-interceptor-3.11.0.jar
 lz4-java-1.5.0.jar
-machinist_2.12-0.6.1.jar
-macro-compat_2.12-1.1.1.jar
+machinist_2.11-0.6.1.jar
+macro-compat_2.11-1.1.1.jar
 metrics-core-3.2.6.jar
 metrics-graphite-3.2.6.jar
 metrics-influxdb-1.2.2.jar
@@ -183,18 +183,18 @@ protobuf-java-2.5.0.jar
 py4j-0.10.8.1.jar
 pyrolite-4.13.jar
 safe-logging-1.5.1.jar
-scala-compiler-2.12.7.jar
-scala-library-2.12.7.jar
-scala-parser-combinators_2.12-1.1.0.jar
-scala-reflect-2.12.7.jar
-scala-xml_2.12-1.0.5.jar
-shapeless_2.12-2.3.2.jar
+scala-compiler-2.11.12.jar
+scala-library-2.11.12.jar
+scala-parser-combinators_2.11-1.1.0.jar
+scala-reflect-2.11.12.jar
+scala-xml_2.11-1.0.5.jar
+shapeless_2.11-2.3.2.jar
 slf4j-api-1.7.25.jar
 slf4j-log4j12-1.7.25.jar
 snakeyaml-1.23.jar
 snappy-java-1.1.7.2.jar
-spire-macros_2.12-0.13.0.jar
-spire_2.12-0.13.0.jar
+spire-macros_2.11-0.13.0.jar
+spire_2.11-0.13.0.jar
 stax-api-1.0-2.jar
 stax2-api-3.1.4.jar
 stream-2.9.6.jar
diff --git a/dev/publish-local.sh b/dev/publish-local.sh
index 4deb8abc74044..e882c379a9d1c 100755
--- a/dev/publish-local.sh
+++ b/dev/publish-local.sh
@@ -11,4 +11,3 @@ set_version_and_install
 DONT_BUILD=true make_dist
 mkdir -p $MVN_LOCAL/org/apache/spark/${artifact_name}/${version}
 cp $file_name $MVN_LOCAL/org/apache/spark/${artifact_name}/${version}/${artifact_name}-${version}.tgz
-
diff --git a/dev/publish_functions.sh b/dev/publish_functions.sh
index 4cfa0bd860fc4..883d5b7a03b56 100644
--- a/dev/publish_functions.sh
+++ b/dev/publish_functions.sh
@@ -33,7 +33,7 @@ publish_artifacts() {
 make_dist() {
   version=$(get_version)
   hadoop_name="hadoop-palantir"
-  artifact_name="spark-dist_2.12-${hadoop_name}"
+  artifact_name="spark-dist_2.11-${hadoop_name}"
   file_name="spark-dist-${version}-${hadoop_name}.tgz"
   ./dev/make-distribution.sh --name "hadoop-palantir" --tgz "$@" "${PALANTIR_FLAGS[@]}"
 }
diff --git a/dists/hadoop-palantir-bom/pom.xml b/dists/hadoop-palantir-bom/pom.xml
index 523997699e9e6..000689efb2583 100644
--- a/dists/hadoop-palantir-bom/pom.xml
+++ b/dists/hadoop-palantir-bom/pom.xml
@@ -20,12 +20,12 @@
     <modelVersion>4.0.0</modelVersion>
     <parent>
         <groupId>org.apache.spark</groupId>
-        <artifactId>spark-parent_2.12</artifactId>
+        <artifactId>spark-parent_2.11</artifactId>
         <version>3.0.0-SNAPSHOT</version>
         <relativePath>../../pom.xml</relativePath>
     </parent>
 
-    <artifactId>spark-dist_2.12-hadoop-palantir-bom</artifactId>
+    <artifactId>spark-dist_2.11-hadoop-palantir-bom</artifactId>
     <name>Spark Project Dist Palantir Hadoop (BOM)</name>
     <url>http://spark.apache.org/</url>
     <packaging>pom</packaging>
diff --git a/dists/hadoop-palantir/pom.xml b/dists/hadoop-palantir/pom.xml
index a3bb85e70f844..9eab8c8a20147 100644
--- a/dists/hadoop-palantir/pom.xml
+++ b/dists/hadoop-palantir/pom.xml
@@ -20,12 +20,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-dist_2.12-hadoop-palantir-bom</artifactId>
+    <artifactId>spark-dist_2.11-hadoop-palantir-bom</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../hadoop-palantir-bom/pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-dist_2.12-hadoop-palantir</artifactId>
+  <artifactId>spark-dist_2.11-hadoop-palantir</artifactId>
   <name>Spark Project Dist Palantir Hadoop</name>
   <url>http://spark.apache.org/</url>
   <packaging>pom</packaging>
diff --git a/docs/_config.yml b/docs/_config.yml
index 649d18bf72b57..c3ef98575fa62 100644
--- a/docs/_config.yml
+++ b/docs/_config.yml
@@ -16,8 +16,8 @@ include:
 # of Spark, Scala, and Mesos.
 SPARK_VERSION: 3.0.0-SNAPSHOT
 SPARK_VERSION_SHORT: 3.0.0
-SCALA_BINARY_VERSION: "2.12"
-SCALA_VERSION: "2.12.7"
+SCALA_BINARY_VERSION: "2.11"
+SCALA_VERSION: "2.11.12"
 MESOS_VERSION: 1.0.0
 SPARK_ISSUE_TRACKER_URL: https://issues.apache.org/jira/browse/SPARK
 SPARK_GITHUB_URL: https://github.com/apache/spark
diff --git a/docs/_plugins/copy_api_dirs.rb b/docs/_plugins/copy_api_dirs.rb
index 2d1a9547e3731..4d0d043a349bb 100644
--- a/docs/_plugins/copy_api_dirs.rb
+++ b/docs/_plugins/copy_api_dirs.rb
@@ -37,7 +37,7 @@
 
     # Copy over the unified ScalaDoc for all projects to api/scala.
     # This directory will be copied over to _site when `jekyll` command is run.
-    source = "../target/scala-2.12/unidoc"
+    source = "../target/scala-2.11/unidoc"
     dest = "api/scala"
 
     puts "Making directory " + dest
diff --git a/examples/pom.xml b/examples/pom.xml
index fbc3ec40359f7..e9b1d4be33974 100644
--- a/examples/pom.xml
+++ b/examples/pom.xml
@@ -20,12 +20,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-examples_2.12</artifactId>
+  <artifactId>spark-examples_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project Examples</name>
   <url>http://spark.apache.org/</url>
diff --git a/external/avro/pom.xml b/external/avro/pom.xml
index ba6f20bfdbf58..9d8f319cc9396 100644
--- a/external/avro/pom.xml
+++ b/external/avro/pom.xml
@@ -20,12 +20,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-avro_2.12</artifactId>
+  <artifactId>spark-avro_2.11</artifactId>
   <properties>
     <sbt.project.name>avro</sbt.project.name>
   </properties>
diff --git a/external/docker-integration-tests/pom.xml b/external/docker-integration-tests/pom.xml
index b39db7540b7d2..f24254b698080 100644
--- a/external/docker-integration-tests/pom.xml
+++ b/external/docker-integration-tests/pom.xml
@@ -21,12 +21,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-docker-integration-tests_2.12</artifactId>
+  <artifactId>spark-docker-integration-tests_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project Docker Integration Tests</name>
   <url>http://spark.apache.org/</url>
diff --git a/external/kafka-0-10-assembly/pom.xml b/external/kafka-0-10-assembly/pom.xml
index f2dcf5d217a89..4f9c3163b2408 100644
--- a/external/kafka-0-10-assembly/pom.xml
+++ b/external/kafka-0-10-assembly/pom.xml
@@ -20,12 +20,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-streaming-kafka-0-10-assembly_2.12</artifactId>
+  <artifactId>spark-streaming-kafka-0-10-assembly_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Integration for Kafka 0.10 Assembly</name>
   <url>http://spark.apache.org/</url>
diff --git a/external/kafka-0-10-sql/pom.xml b/external/kafka-0-10-sql/pom.xml
index 1af407167597b..9696dff69d8b0 100644
--- a/external/kafka-0-10-sql/pom.xml
+++ b/external/kafka-0-10-sql/pom.xml
@@ -20,13 +20,13 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
   <groupId>org.apache.spark</groupId>
-  <artifactId>spark-sql-kafka-0-10_2.12</artifactId>
+  <artifactId>spark-sql-kafka-0-10_2.11</artifactId>
   <properties>
     <sbt.project.name>sql-kafka-0-10</sbt.project.name>
     <!-- note that this should be compatible with Kafka brokers version 0.10 and up -->
diff --git a/external/kafka-0-10/pom.xml b/external/kafka-0-10/pom.xml
index ea18b7e035915..0cd49480314d5 100644
--- a/external/kafka-0-10/pom.xml
+++ b/external/kafka-0-10/pom.xml
@@ -20,12 +20,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-streaming-kafka-0-10_2.12</artifactId>
+  <artifactId>spark-streaming-kafka-0-10_2.11</artifactId>
   <properties>
     <sbt.project.name>streaming-kafka-0-10</sbt.project.name>
     <!-- note that this should be compatible with Kafka brokers version 0.10 and up -->
diff --git a/external/kinesis-asl-assembly/pom.xml b/external/kinesis-asl-assembly/pom.xml
index 0ce922349ea66..0bf4c265939e7 100644
--- a/external/kinesis-asl-assembly/pom.xml
+++ b/external/kinesis-asl-assembly/pom.xml
@@ -20,12 +20,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-streaming-kinesis-asl-assembly_2.12</artifactId>
+  <artifactId>spark-streaming-kinesis-asl-assembly_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project Kinesis Assembly</name>
   <url>http://spark.apache.org/</url>
diff --git a/external/kinesis-asl/pom.xml b/external/kinesis-asl/pom.xml
index 7d69764b77de7..0aef25329db99 100644
--- a/external/kinesis-asl/pom.xml
+++ b/external/kinesis-asl/pom.xml
@@ -19,13 +19,13 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
   <!-- Kinesis integration is not included by default due to ASL-licensed code. -->
-  <artifactId>spark-streaming-kinesis-asl_2.12</artifactId>
+  <artifactId>spark-streaming-kinesis-asl_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Kinesis Integration</name>
 
diff --git a/external/spark-ganglia-lgpl/pom.xml b/external/spark-ganglia-lgpl/pom.xml
index a23d255f9187c..35a55b70baf33 100644
--- a/external/spark-ganglia-lgpl/pom.xml
+++ b/external/spark-ganglia-lgpl/pom.xml
@@ -19,13 +19,13 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
   <!-- Ganglia integration is not included by default due to LGPL-licensed code -->
-  <artifactId>spark-ganglia-lgpl_2.12</artifactId>
+  <artifactId>spark-ganglia-lgpl_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Ganglia Integration</name>
 
diff --git a/graphx/pom.xml b/graphx/pom.xml
index 444568a03d6c7..22bc148e068a5 100644
--- a/graphx/pom.xml
+++ b/graphx/pom.xml
@@ -20,12 +20,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-graphx_2.12</artifactId>
+  <artifactId>spark-graphx_2.11</artifactId>
   <properties>
     <sbt.project.name>graphx</sbt.project.name>
   </properties>
diff --git a/hadoop-cloud/pom.xml b/hadoop-cloud/pom.xml
index fb343f3fb937d..0335724c36f55 100644
--- a/hadoop-cloud/pom.xml
+++ b/hadoop-cloud/pom.xml
@@ -21,12 +21,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-hadoop-cloud_2.12</artifactId>
+  <artifactId>spark-hadoop-cloud_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project Cloud Integration</name>
   <description>
diff --git a/launcher/pom.xml b/launcher/pom.xml
index 130519d6c3b08..a833a35399918 100644
--- a/launcher/pom.xml
+++ b/launcher/pom.xml
@@ -21,12 +21,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-launcher_2.12</artifactId>
+  <artifactId>spark-launcher_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project Launcher</name>
   <url>http://spark.apache.org/</url>
diff --git a/mllib-local/pom.xml b/mllib-local/pom.xml
index 2eab868ac0dc8..ec5f9b0e92c8f 100644
--- a/mllib-local/pom.xml
+++ b/mllib-local/pom.xml
@@ -20,12 +20,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-mllib-local_2.12</artifactId>
+  <artifactId>spark-mllib-local_2.11</artifactId>
   <properties>
     <sbt.project.name>mllib-local</sbt.project.name>
   </properties>
diff --git a/mllib/pom.xml b/mllib/pom.xml
index 0b17345064a71..17ddb87c4d86a 100644
--- a/mllib/pom.xml
+++ b/mllib/pom.xml
@@ -20,12 +20,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-mllib_2.12</artifactId>
+  <artifactId>spark-mllib_2.11</artifactId>
   <properties>
     <sbt.project.name>mllib</sbt.project.name>
   </properties>
diff --git a/pom.xml b/pom.xml
index d9899108fb5e9..bce60fc97d0ba 100644
--- a/pom.xml
+++ b/pom.xml
@@ -25,7 +25,7 @@
     <version>18</version>
   </parent>
   <groupId>org.apache.spark</groupId>
-  <artifactId>spark-parent_2.12</artifactId>
+  <artifactId>spark-parent_2.11</artifactId>
   <version>3.0.0-SNAPSHOT</version>
   <packaging>pom</packaging>
   <name>Spark Project Parent POM</name>
@@ -170,8 +170,8 @@
     <commons.math3.version>3.6.1</commons.math3.version>
     <!-- managed up from 3.2.1 for SPARK-11652 -->
     <commons.collections.version>3.2.2</commons.collections.version>
-    <scala.version>2.12.7</scala.version>
-    <scala.binary.version>2.12</scala.binary.version>
+    <scala.version>2.11.12</scala.version>
+    <scala.binary.version>2.11</scala.binary.version>
     <codehaus.jackson.version>1.9.13</codehaus.jackson.version>
     <fasterxml.jackson.version>2.9.7</fasterxml.jackson.version>
     <snappy.version>1.1.7.2</snappy.version>
@@ -2308,7 +2308,6 @@
                       -->
                       <exclude>org.jboss.netty</exclude>
                       <exclude>org.codehaus.groovy</exclude>
-                      <exclude>*:*_2.11</exclude>
                       <exclude>*:*_2.10</exclude>
                     </excludes>
                     <searchTransitive>true</searchTransitive>
@@ -3034,14 +3033,14 @@
 
     <!-- Exists for backwards compatibility; profile doesn't do anything -->
     <profile>
-      <id>scala-2.12</id>
+      <id>scala-2.11</id>
     </profile>
 
     <profile>
-      <id>scala-2.11</id>
+      <id>scala-2.12</id>
       <properties>
-        <scala.version>2.11.12</scala.version>
-        <scala.binary.version>2.11</scala.binary.version>
+        <scala.version>2.12.7</scala.version>
+        <scala.binary.version>2.12</scala.binary.version>
       </properties>
       <build>
         <plugins>
@@ -3057,9 +3056,8 @@
                 <configuration>
                   <rules>
                     <bannedDependencies>
-                      <excludes combine.self="override">
-                        <exclude>org.jboss.netty</exclude>
-                        <exclude>org.codehaus.groovy</exclude>
+                      <excludes combine.children="append">
+                        <exclude>*:*_2.11</exclude>
                         <exclude>*:*_2.10</exclude>
                       </excludes>
                     </bannedDependencies>
diff --git a/project/MimaBuild.scala b/project/MimaBuild.scala
index 10c02103aeddb..79e6745977e5b 100644
--- a/project/MimaBuild.scala
+++ b/project/MimaBuild.scala
@@ -90,7 +90,7 @@ object MimaBuild {
     val organization = "org.apache.spark"
     val previousSparkVersion = "2.4.0"
     val project = projectRef.project
-    val fullId = "spark-" + project + "_2.12"
+    val fullId = "spark-" + project + "_2.11"
     mimaDefaultSettings ++
     Seq(mimaPreviousArtifacts := Set(organization % fullId % previousSparkVersion),
       mimaBinaryIssueFilters ++= ignoredABIProblems(sparkHome, version.value))
diff --git a/project/SparkBuild.scala b/project/SparkBuild.scala
index 639d642b78d2a..35108f1341858 100644
--- a/project/SparkBuild.scala
+++ b/project/SparkBuild.scala
@@ -96,15 +96,15 @@ object SparkBuild extends PomBuild {
     }
 
     Option(System.getProperty("scala.version"))
-      .filter(_.startsWith("2.11"))
+      .filter(_.startsWith("2.12"))
       .foreach { versionString =>
-        System.setProperty("scala-2.11", "true")
+        System.setProperty("scala-2.12", "true")
       }
-    if (System.getProperty("scala-2.11") == "") {
+    if (System.getProperty("scala-2.12") == "") {
       // To activate scala-2.10 profile, replace empty property value to non-empty value
       // in the same way as Maven which handles -Dname as -Dname=true before executes build process.
       // see: https://github.com/apache/maven/blob/maven-3.0.4/maven-embedder/src/main/java/org/apache/maven/cli/MavenCli.java#L1082
-      System.setProperty("scala-2.11", "true")
+      System.setProperty("scala-2.12", "true")
     }
     profiles
   }
@@ -857,10 +857,10 @@ object TestSettings {
   import BuildCommons._
 
   private val scalaBinaryVersion =
-    if (System.getProperty("scala-2.11") == "true") {
-      "2.11"
-    } else {
+    if (System.getProperty("scala-2.12") == "true") {
       "2.12"
+    } else {
+      "2.11"
     }
   lazy val settings = Seq (
     // Fork new JVMs for tests and set Java options for those
diff --git a/python/run-tests.py b/python/run-tests.py
index be5a60a28def6..f4eda6ee9ad06 100755
--- a/python/run-tests.py
+++ b/python/run-tests.py
@@ -60,7 +60,9 @@ def print_red(text):
 LOGGER = logging.getLogger()
 
 # Find out where the assembly jars are located.
-for scala in ["2.11", "2.12"]:
+# Later, add back 2.12 to this list:
+# for scala in ["2.11", "2.12"]:
+for scala in ["2.11"]:
     build_dir = os.path.join(SPARK_HOME, "assembly", "target", "scala-" + scala)
     if os.path.isdir(build_dir):
         SPARK_DIST_CLASSPATH = os.path.join(build_dir, "jars", "*")
diff --git a/repl/pom.xml b/repl/pom.xml
index c7de67e41ca94..fa015b69d45d4 100644
--- a/repl/pom.xml
+++ b/repl/pom.xml
@@ -20,12 +20,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-repl_2.12</artifactId>
+  <artifactId>spark-repl_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project REPL</name>
   <url>http://spark.apache.org/</url>
diff --git a/resource-managers/kubernetes/core/pom.xml b/resource-managers/kubernetes/core/pom.xml
index 8d594ee8f1478..b89ea383bf872 100644
--- a/resource-managers/kubernetes/core/pom.xml
+++ b/resource-managers/kubernetes/core/pom.xml
@@ -19,12 +19,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../../../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-kubernetes_2.12</artifactId>
+  <artifactId>spark-kubernetes_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project Kubernetes</name>
   <properties>
diff --git a/resource-managers/kubernetes/integration-tests/pom.xml b/resource-managers/kubernetes/integration-tests/pom.xml
index 17af0e03f2bbb..301b6fe8eee56 100644
--- a/resource-managers/kubernetes/integration-tests/pom.xml
+++ b/resource-managers/kubernetes/integration-tests/pom.xml
@@ -19,12 +19,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../../../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-kubernetes-integration-tests_2.12</artifactId>
+  <artifactId>spark-kubernetes-integration-tests_2.11</artifactId>
   <properties>
     <download-maven-plugin.version>1.3.0</download-maven-plugin.version>
     <exec-maven-plugin.version>1.4.0</exec-maven-plugin.version>
diff --git a/resource-managers/mesos/pom.xml b/resource-managers/mesos/pom.xml
index 7b3aad4d6ce35..9585bdfafdcf4 100644
--- a/resource-managers/mesos/pom.xml
+++ b/resource-managers/mesos/pom.xml
@@ -19,12 +19,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-mesos_2.12</artifactId>
+  <artifactId>spark-mesos_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project Mesos</name>
   <properties>
diff --git a/resource-managers/yarn/pom.xml b/resource-managers/yarn/pom.xml
index d18df9955bb1f..e55b814be8465 100644
--- a/resource-managers/yarn/pom.xml
+++ b/resource-managers/yarn/pom.xml
@@ -19,12 +19,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-yarn_2.12</artifactId>
+  <artifactId>spark-yarn_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project YARN</name>
   <properties>
diff --git a/sql/catalyst/pom.xml b/sql/catalyst/pom.xml
index 20cc5d03fbe52..16ecebf159c1f 100644
--- a/sql/catalyst/pom.xml
+++ b/sql/catalyst/pom.xml
@@ -21,12 +21,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-catalyst_2.12</artifactId>
+  <artifactId>spark-catalyst_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project Catalyst</name>
   <url>http://spark.apache.org/</url>
diff --git a/sql/core/pom.xml b/sql/core/pom.xml
index ac5f1fc923e7d..95e98c5444721 100644
--- a/sql/core/pom.xml
+++ b/sql/core/pom.xml
@@ -21,12 +21,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-sql_2.12</artifactId>
+  <artifactId>spark-sql_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project SQL</name>
   <url>http://spark.apache.org/</url>
diff --git a/sql/hive-thriftserver/pom.xml b/sql/hive-thriftserver/pom.xml
index 4a4629fae2706..55e051c3ed1be 100644
--- a/sql/hive-thriftserver/pom.xml
+++ b/sql/hive-thriftserver/pom.xml
@@ -21,12 +21,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-hive-thriftserver_2.12</artifactId>
+  <artifactId>spark-hive-thriftserver_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project Hive Thrift Server</name>
   <url>http://spark.apache.org/</url>
diff --git a/sql/hive/pom.xml b/sql/hive/pom.xml
index 9642e5e3d035a..114a108ba2752 100644
--- a/sql/hive/pom.xml
+++ b/sql/hive/pom.xml
@@ -21,12 +21,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-hive_2.12</artifactId>
+  <artifactId>spark-hive_2.11</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project Hive</name>
   <url>http://spark.apache.org/</url>
diff --git a/streaming/pom.xml b/streaming/pom.xml
index 1d1ea469f7d18..f9a5029a8e818 100644
--- a/streaming/pom.xml
+++ b/streaming/pom.xml
@@ -20,12 +20,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-streaming_2.12</artifactId>
+  <artifactId>spark-streaming_2.11</artifactId>
   <properties>
     <sbt.project.name>streaming</sbt.project.name>
   </properties>
diff --git a/tools/pom.xml b/tools/pom.xml
index 6286fad403c83..247f5a6df4b08 100644
--- a/tools/pom.xml
+++ b/tools/pom.xml
@@ -19,12 +19,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.11</artifactId>
     <version>3.0.0-SNAPSHOT</version>
     <relativePath>../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-tools_2.12</artifactId>
+  <artifactId>spark-tools_2.11</artifactId>
   <properties>
     <sbt.project.name>tools</sbt.project.name>
   </properties>