diff --git a/Makefile b/Makefile
index 9a25aefe7e34c..6f5db6acd4077 100644
--- a/Makefile
+++ b/Makefile
@@ -9,26 +9,26 @@ julia-debug julia-release:
 	@$(MAKE) -sC external
 	@$(MAKE) -sC src lib$@
 	@$(MAKE) -sC ui $@
-	@$(MAKE) -sC j
+	@$(MAKE) -sC jl
 	@ln -f $@-$(DEFAULT_REPL) julia
 
-sys0.ji: src/boot.j src/dump.c j/stage0.j
-	$(QUIET_JULIA) ./julia -b stage0.j
+sys0.ji: src/boot.jl src/dump.c jl/stage0.jl
+	$(QUIET_JULIA) ./julia -b stage0.jl
 	@rm -f sys.ji
 
 # if sys.ji exists, use it to rebuild, otherwise use sys0.ji
-sys.ji: VERSION sys0.ji j/stage1.j j/sysimg.j j/start_image.j j/*.j
-	$(QUIET_JULIA) ./julia `test -f sys.ji && echo stage1.j || echo -J sys0.ji stage1.j`
+sys.ji: VERSION sys0.ji jl/stage1.jl jl/sysimg.jl jl/start_image.jl jl/*.jl
+	$(QUIET_JULIA) ./julia `test -f sys.ji && echo stage1.jl || echo -J sys0.ji stage1.jl`
 
 install: release
 	install -d $(DESTDIR)$(PREFIX)/share/julia/lib
-	install -d $(DESTDIR)$(PREFIX)/share/julia/j
+	install -d $(DESTDIR)$(PREFIX)/share/julia/jl
 	install -d $(DESTDIR)$(PREFIX)/share/julia/contrib
 	install -d $(DESTDIR)$(PREFIX)/share/julia/examples
 	install -v julia* $(DESTDIR)$(PREFIX)/share/julia
 	install -v sys.ji $(DESTDIR)$(PREFIX)/share/julia
-	install -v j/* $(DESTDIR)$(PREFIX)/share/julia/j
-	install -v examples/*.j $(DESTDIR)$(PREFIX)/share/julia/examples
+	install -v jl/* $(DESTDIR)$(PREFIX)/share/julia/jl
+	install -v examples/*.jl $(DESTDIR)$(PREFIX)/share/julia/examples
 	install -v lib/libarpack.$(SHLIB_EXT) lib/libfdm.$(SHLIB_EXT) lib/libfftw3.$(SHLIB_EXT)* lib/libfftw3f.$(SHLIB_EXT)* lib/libpcre.$(SHLIB_EXT)* lib/libpcrecpp.$(SHLIB_EXT)* lib/libpcreposix.$(SHLIB_EXT)* lib/librandom.$(SHLIB_EXT) lib/liblapack.$(SHLIB_EXT) lib/libsuitesparse*$(SHLIB_EXT) lib/libgrisu.$(SHLIB_EXT) lib/libamos.$(SHLIB_EXT) $(DESTDIR)$(PREFIX)/share/julia/lib
 
 dist: release
@@ -50,7 +50,7 @@ clean:
 	@rm -f *~ *#
 	@rm -f sys0.ji
 	@rm -f sys.ji
-	@$(MAKE) -sC j clean
+	@$(MAKE) -sC jl clean
 	@$(MAKE) -sC src clean
 	@$(MAKE) -sC ui clean
 	@$(MAKE) -sC ui/webserver clean
diff --git a/attic/doc/ipc.j b/attic/doc/ipc.jl
similarity index 100%
rename from attic/doc/ipc.j
rename to attic/doc/ipc.jl
diff --git a/attic/doc/quickstart.j b/attic/doc/quickstart.jl
similarity index 100%
rename from attic/doc/quickstart.j
rename to attic/doc/quickstart.jl
diff --git a/attic/ec2.j b/attic/ec2.jl
similarity index 100%
rename from attic/ec2.j
rename to attic/ec2.jl
diff --git a/attic/vcloud.j b/attic/vcloud.jl
similarity index 100%
rename from attic/vcloud.j
rename to attic/vcloud.jl
diff --git a/examples/bigfib.j b/examples/bigfib.jl
similarity index 100%
rename from examples/bigfib.j
rename to examples/bigfib.jl
diff --git a/examples/bitvector.j b/examples/bitvector.jl
similarity index 100%
rename from examples/bitvector.j
rename to examples/bitvector.jl
diff --git a/examples/blksvd.j b/examples/blksvd.jl
similarity index 100%
rename from examples/blksvd.j
rename to examples/blksvd.jl
diff --git a/examples/colorimetry.j b/examples/colorimetry.jl
similarity index 100%
rename from examples/colorimetry.j
rename to examples/colorimetry.jl
diff --git a/examples/dsparsemat.j b/examples/dsparsemat.jl
similarity index 100%
rename from examples/dsparsemat.j
rename to examples/dsparsemat.jl
diff --git a/examples/graph.j b/examples/graph.jl
similarity index 100%
rename from examples/graph.j
rename to examples/graph.jl
diff --git a/examples/image.j b/examples/image.jl
similarity index 100%
rename from examples/image.j
rename to examples/image.jl
diff --git a/examples/list.j b/examples/list.jl
similarity index 100%
rename from examples/list.j
rename to examples/list.jl
diff --git a/examples/math_openlibm.j b/examples/math_openlibm.jl
similarity index 100%
rename from examples/math_openlibm.j
rename to examples/math_openlibm.jl
diff --git a/examples/median.j b/examples/median.jl
similarity index 100%
rename from examples/median.j
rename to examples/median.jl
diff --git a/examples/ndgrid.j b/examples/ndgrid.jl
similarity index 100%
rename from examples/ndgrid.j
rename to examples/ndgrid.jl
diff --git a/examples/ndrange.j b/examples/ndrange.jl
similarity index 100%
rename from examples/ndrange.j
rename to examples/ndrange.jl
diff --git a/examples/preduce.j b/examples/preduce.jl
similarity index 100%
rename from examples/preduce.j
rename to examples/preduce.jl
diff --git a/examples/quaternion.j b/examples/quaternion.jl
similarity index 100%
rename from examples/quaternion.j
rename to examples/quaternion.jl
diff --git a/examples/queue.j b/examples/queue.jl
similarity index 100%
rename from examples/queue.j
rename to examples/queue.jl
diff --git a/examples/rmt/chapter1.j b/examples/rmt/chapter1.jl
similarity index 100%
rename from examples/rmt/chapter1.j
rename to examples/rmt/chapter1.jl
diff --git a/examples/rmt/chapter2.j b/examples/rmt/chapter2.jl
similarity index 100%
rename from examples/rmt/chapter2.j
rename to examples/rmt/chapter2.jl
diff --git a/examples/specfun.j b/examples/specfun.jl
similarity index 100%
rename from examples/specfun.j
rename to examples/specfun.jl
diff --git a/examples/tree.j b/examples/tree.jl
similarity index 100%
rename from examples/tree.j
rename to examples/tree.jl
diff --git a/examples/wordcount.j b/examples/wordcount.jl
similarity index 100%
rename from examples/wordcount.j
rename to examples/wordcount.jl
diff --git a/examples/ziggurat.j b/examples/ziggurat.jl
similarity index 100%
rename from examples/ziggurat.j
rename to examples/ziggurat.jl
diff --git a/j/.gitignore b/jl/.gitignore
similarity index 100%
rename from j/.gitignore
rename to jl/.gitignore
diff --git a/j/Makefile b/jl/Makefile
similarity index 83%
rename from j/Makefile
rename to jl/Makefile
index 7db3ab0f03c4a..9aec0dd57d94d 100644
--- a/j/Makefile
+++ b/jl/Makefile
@@ -3,15 +3,15 @@ include ../Make.inc
 
 PCRE_CONST = 0x[0-9a-fA-F]+|[-+]?\s*[0-9]+
 
-all: pcre_h.j errno_h.j
+all: pcre_h.jl errno_h.jl
 
-pcre_h.j:
+pcre_h.jl:
 	$(QUIET_PERL) cpp -dM $(shell $(PCRE_CONFIG) --prefix)/include/pcre.h | perl -nle '/^\s*#define\s+(PCRE\w*)\s*\(?($(PCRE_CONST))\)?\s*$$/ and print "const $$1 = int32($$2)"' | sort > $@
 
-errno_h.j:
+errno_h.jl:
 	$(QUIET_PERL) echo '#include "errno.h"' | cpp -dM - | perl -nle 'print "const $$1 = int32($$2)" if /^#define\s+(E\w+)\s+(\d+)\s*$$/' | sort > $@
 
 clean:
 	rm -f *# *~
-	rm -f pcre_h.j
-	rm -f errno_h.j
+	rm -f pcre_h.jl
+	rm -f errno_h.jl
diff --git a/j/abstractarray.j b/jl/abstractarray.jl
similarity index 99%
rename from j/abstractarray.j
rename to jl/abstractarray.jl
index 54cbe92434425..2da91f452fe8a 100644
--- a/j/abstractarray.j
+++ b/jl/abstractarray.jl
@@ -1,4 +1,4 @@
-## abstractarray.j : Generic array interfaces.
+## abstractarray.jl : Generic array interfaces.
 
 ## Type aliases for convenience ##
 
diff --git a/j/array.j b/jl/array.jl
similarity index 99%
rename from j/array.j
rename to jl/array.jl
index 7f9d27d820910..3814d0d5115ee 100644
--- a/j/array.j
+++ b/jl/array.jl
@@ -1,4 +1,4 @@
-## array.j: Dense arrays
+## array.jl: Dense arrays
 
 typealias Vector{T} Array{T,1}
 typealias Matrix{T} Array{T,2}
diff --git a/j/ascii.j b/jl/ascii.jl
similarity index 98%
rename from j/ascii.j
rename to jl/ascii.jl
index 86067d2f94b3d..1d3aef16d3988 100644
--- a/j/ascii.j
+++ b/jl/ascii.jl
@@ -1,4 +1,4 @@
-## from src/boot.j
+## from src/boot.jl
 # type ASCIIString <: DirectIndexString; data::Array{Uint8,1}; end
 
 ## required core functionality ##
diff --git a/j/base.j b/jl/base.jl
similarity index 100%
rename from j/base.j
rename to jl/base.jl
diff --git a/j/bigint.j b/jl/bigint.jl
similarity index 100%
rename from j/bigint.j
rename to jl/bigint.jl
diff --git a/j/bool.j b/jl/bool.jl
similarity index 100%
rename from j/bool.j
rename to jl/bool.jl
diff --git a/j/cell.j b/jl/cell.jl
similarity index 100%
rename from j/cell.j
rename to jl/cell.jl
diff --git a/j/char.j b/jl/char.jl
similarity index 100%
rename from j/char.j
rename to jl/char.jl
diff --git a/j/client.j b/jl/client.jl
similarity index 97%
rename from j/client.j
rename to jl/client.jl
index 15e86005aba75..117763d668b0c 100644
--- a/j/client.j
+++ b/jl/client.jl
@@ -1,5 +1,5 @@
-## client.j - frontend handling command line options, environment setup,
-##            and REPL
+## client.jl - frontend handling command line options, environment setup,
+##             and REPL
 
 const _jl_color_normal = "\033[0m"
 
@@ -196,10 +196,10 @@ function _start()
         end
 
         global const VARIABLES = {}
-        global const LOAD_PATH = String["", "$JULIA_HOME/", "$JULIA_HOME/j/"]
+        global const LOAD_PATH = String["", "$JULIA_HOME/", "$JULIA_HOME/jl/"]
 
         # Load customized startup
-        try include(strcat(getcwd(),"/startup.j")) end
+        try include(strcat(getcwd(),"/startup.jl")) end
         try include(strcat(ENV["HOME"],"/.juliarc")) end
 
         (quiet,repl) = process_options(ARGS)
diff --git a/j/combinatorics.j b/jl/combinatorics.jl
similarity index 100%
rename from j/combinatorics.j
rename to jl/combinatorics.jl
diff --git a/j/complex.j b/jl/complex.jl
similarity index 100%
rename from j/complex.j
rename to jl/complex.jl
diff --git a/j/darray.j b/jl/darray.jl
similarity index 100%
rename from j/darray.j
rename to jl/darray.jl
diff --git a/j/datafmt.j b/jl/datafmt.jl
similarity index 100%
rename from j/datafmt.j
rename to jl/datafmt.jl
diff --git a/j/env.j b/jl/env.jl
similarity index 100%
rename from j/env.j
rename to jl/env.jl
diff --git a/j/error.j b/jl/error.jl
similarity index 100%
rename from j/error.j
rename to jl/error.jl
diff --git a/j/expr.j b/jl/expr.jl
similarity index 100%
rename from j/expr.j
rename to jl/expr.jl
diff --git a/j/float.j b/jl/float.jl
similarity index 100%
rename from j/float.j
rename to jl/float.jl
diff --git a/j/floatfuncs.j b/jl/floatfuncs.jl
similarity index 100%
rename from j/floatfuncs.j
rename to jl/floatfuncs.jl
diff --git a/j/grisu.j b/jl/grisu.jl
similarity index 100%
rename from j/grisu.j
rename to jl/grisu.jl
diff --git a/j/inference.j b/jl/inference.jl
similarity index 99%
rename from j/inference.j
rename to jl/inference.jl
index dad1792b16945..71b872b32e37f 100644
--- a/j/inference.j
+++ b/jl/inference.jl
@@ -674,7 +674,7 @@ function _jl_abstract_interpret(e::Expr, vtypes, sv::StaticVarInfo)
         if isa(lhs,SymbolNode)
             lhs = lhs.name
         end
-        assert(isa(lhs,Symbol), "inference.j:579")
+        assert(isa(lhs,Symbol), "inference.jl:579")
         return StateUpdate(lhs, t, vtypes)
     elseif is(e.head,:call) || is(e.head,:call1)
         abstract_eval(e, vtypes, sv)
@@ -884,7 +884,7 @@ function typeinf(linfo::LambdaStaticData,atypes::Tuple,sparams::Tuple, def, cop)
 
     args = f_argnames(ast)
     la = length(args)
-    assert(is(ast.head,:lambda), "inference.j:745")
+    assert(is(ast.head,:lambda), "inference.jl:745")
     locals = (ast.args[2][1])::Array{Any,1}
     vars = append(args, locals)
     body = (ast.args[3].args)::Array{Any,1}
@@ -1326,8 +1326,8 @@ function inlineable(f, e::Expr, vars)
     if length(body) != 1
         return NF
     end
-    assert(isa(body[1],Expr), "inference.j:1050")
-    assert(is(body[1].head,:return), "inference.j:1051")
+    assert(isa(body[1],Expr), "inference.jl:1050")
+    assert(is(body[1].head,:return), "inference.jl:1051")
     # check for vararg function
     args = f_argnames(ast)
     na = length(args)
diff --git a/j/int.j b/jl/int.jl
similarity index 100%
rename from j/int.j
rename to jl/int.jl
diff --git a/j/intfuncs.j b/jl/intfuncs.jl
similarity index 100%
rename from j/intfuncs.j
rename to jl/intfuncs.jl
diff --git a/j/intset.j b/jl/intset.jl
similarity index 100%
rename from j/intset.j
rename to jl/intset.jl
diff --git a/j/io.j b/jl/io.jl
similarity index 100%
rename from j/io.j
rename to jl/io.jl
diff --git a/j/iterator.j b/jl/iterator.jl
similarity index 100%
rename from j/iterator.j
rename to jl/iterator.jl
diff --git a/j/latin1.j b/jl/latin1.jl
similarity index 100%
rename from j/latin1.j
rename to jl/latin1.jl
diff --git a/j/libc.j b/jl/libc.jl
similarity index 100%
rename from j/libc.j
rename to jl/libc.jl
diff --git a/j/linalg.j b/jl/linalg.jl
similarity index 98%
rename from j/linalg.j
rename to jl/linalg.jl
index 79a57f6897cb5..02a3a50c70b11 100644
--- a/j/linalg.j
+++ b/jl/linalg.jl
@@ -1,4 +1,4 @@
-## linalg.j: Basic Linear Algebra functions ##
+## linalg.jl: Basic Linear Algebra functions ##
 
 aCb(x::AbstractVector, y::AbstractVector) = [dot(x, y)]
 aTb{T<:Real}(x::AbstractVector{T}, y::AbstractVector{T}) = [dot(x, y)]
@@ -14,7 +14,7 @@ end
 cross(a::AbstractVector, b::AbstractVector) =
     [a[2]*b[3]-a[3]*b[2], a[3]*b[1]-a[1]*b[3], a[1]*b[2]-a[2]*b[1]]
 
-# blas.j defines matmul for floats; other integer and mixed precision
+# blas.jl defines matmul for floats; other integer and mixed precision
 # cases are handled here
 
 # TODO: It will be faster for large matrices to convert to float,
diff --git a/j/linalg_arpack.j b/jl/linalg_arpack.jl
similarity index 100%
rename from j/linalg_arpack.j
rename to jl/linalg_arpack.jl
diff --git a/j/linalg_blas.j b/jl/linalg_blas.jl
similarity index 100%
rename from j/linalg_blas.j
rename to jl/linalg_blas.jl
diff --git a/j/linalg_lapack.j b/jl/linalg_lapack.jl
similarity index 100%
rename from j/linalg_lapack.j
rename to jl/linalg_lapack.jl
diff --git a/j/linalg_suitesparse.j b/jl/linalg_suitesparse.jl
similarity index 100%
rename from j/linalg_suitesparse.j
rename to jl/linalg_suitesparse.jl
diff --git a/j/math.j b/jl/math.jl
similarity index 100%
rename from j/math.j
rename to jl/math.jl
diff --git a/j/math_libm.j b/jl/math_libm.jl
similarity index 100%
rename from j/math_libm.j
rename to jl/math_libm.jl
diff --git a/j/multi.j b/jl/multi.jl
similarity index 99%
rename from j/multi.j
rename to jl/multi.jl
index 1ae4f64625a7f..bf1bedb94aa23 100644
--- a/j/multi.j
+++ b/jl/multi.jl
@@ -1,4 +1,4 @@
-## multi.j - multiprocessing
+## multi.jl - multiprocessing
 ##
 ## julia starts with one process, and processors can be added using:
 ##   addprocs_local(n)                     using exec
@@ -1092,7 +1092,7 @@ end
 addprocs_sge(n) = add_workers(PGRP, start_sge_workers(n))
 SGE(n) = addprocs_sge(n)
 
-#include("vcloud.j")
+#include("vcloud.jl")
 
 ## global objects and collective operations ##
 
diff --git a/j/number.j b/jl/number.jl
similarity index 100%
rename from j/number.j
rename to jl/number.jl
diff --git a/j/ode.j b/jl/ode.jl
similarity index 100%
rename from j/ode.j
rename to jl/ode.jl
diff --git a/j/operators.j b/jl/operators.jl
similarity index 100%
rename from j/operators.j
rename to jl/operators.jl
diff --git a/j/pcre.j b/jl/pcre.jl
similarity index 99%
rename from j/pcre.j
rename to jl/pcre.jl
index 09ba51d185411..924ad2ab0d340 100644
--- a/j/pcre.j
+++ b/jl/pcre.jl
@@ -1,6 +1,6 @@
 ## low-level pcre interface ##
 
-include("pcre_h.j")
+include("pcre_h.jl")
 
 _jl_libpcre = dlopen("libpcre")
 
diff --git a/j/pointer.j b/jl/pointer.jl
similarity index 100%
rename from j/pointer.j
rename to jl/pointer.jl
diff --git a/j/printf.j b/jl/printf.jl
similarity index 100%
rename from j/printf.j
rename to jl/printf.jl
diff --git a/j/process.j b/jl/process.jl
similarity index 100%
rename from j/process.j
rename to jl/process.jl
diff --git a/j/promotion.j b/jl/promotion.jl
similarity index 100%
rename from j/promotion.j
rename to jl/promotion.jl
diff --git a/j/random.j b/jl/random.jl
similarity index 100%
rename from j/random.j
rename to jl/random.jl
diff --git a/j/range.j b/jl/range.jl
similarity index 100%
rename from j/range.j
rename to jl/range.jl
diff --git a/j/rational.j b/jl/rational.jl
similarity index 100%
rename from j/rational.j
rename to jl/rational.jl
diff --git a/j/reduce.j b/jl/reduce.jl
similarity index 100%
rename from j/reduce.j
rename to jl/reduce.jl
diff --git a/j/regex.j b/jl/regex.jl
similarity index 99%
rename from j/regex.j
rename to jl/regex.jl
index e51120d2e29b8..3eed29d42a3e0 100644
--- a/j/regex.j
+++ b/jl/regex.jl
@@ -1,4 +1,4 @@
-include("pcre.j")
+include("pcre.jl")
 
 ## object-oriented Regex interface ##
 
diff --git a/j/serialize.j b/jl/serialize.jl
similarity index 100%
rename from j/serialize.j
rename to jl/serialize.jl
diff --git a/j/set.j b/jl/set.jl
similarity index 100%
rename from j/set.j
rename to jl/set.jl
diff --git a/j/show.j b/jl/show.jl
similarity index 100%
rename from j/show.j
rename to jl/show.jl
diff --git a/j/signal.j b/jl/signal.jl
similarity index 100%
rename from j/signal.j
rename to jl/signal.jl
diff --git a/j/signal_fftw.j b/jl/signal_fftw.jl
similarity index 100%
rename from j/signal_fftw.j
rename to jl/signal_fftw.jl
diff --git a/j/sort.j b/jl/sort.jl
similarity index 100%
rename from j/sort.j
rename to jl/sort.jl
diff --git a/j/sparse.j b/jl/sparse.jl
similarity index 100%
rename from j/sparse.j
rename to jl/sparse.jl
diff --git a/j/stage0.j b/jl/stage0.jl
similarity index 93%
rename from j/stage0.j
rename to jl/stage0.jl
index 0b5eb6133f3f8..363ab6244b165 100644
--- a/j/stage0.j
+++ b/jl/stage0.jl
@@ -27,9 +27,9 @@ if true
     end
 end
 
-include("sysimg.j")
+include("sysimg.jl")
 
 ccall(:jl_save_system_image, Void, (Ptr{Uint8},Ptr{Uint8}),
-      cstring("sys0.ji"), cstring("j/start_image.j"))
+      cstring("sys0.ji"), cstring("jl/start_image.jl"))
 
 end # module
diff --git a/j/stage1.j b/jl/stage1.jl
similarity index 84%
rename from j/stage1.j
rename to jl/stage1.jl
index e17b706c2b7a3..1d950dd695f71 100644
--- a/j/stage1.j
+++ b/jl/stage1.jl
@@ -1,6 +1,6 @@
 module NewSystem
 
-include("sysimg.j")
+include("sysimg.jl")
 
 # invoke type inference, running the existing inference code on the new
 # inference code to cache an optimized version of it.
@@ -11,6 +11,6 @@ begin
 end
 
 ccall(:jl_save_system_image, Void, (Ptr{Uint8},Ptr{Uint8}),
-      cstring("sys.ji"), cstring("j/start_image.j"))
+      cstring("sys.ji"), cstring("jl/start_image.jl"))
 
 end # module
diff --git a/j/start_image.j b/jl/start_image.jl
similarity index 100%
rename from j/start_image.j
rename to jl/start_image.jl
diff --git a/j/statistics.j b/jl/statistics.jl
similarity index 100%
rename from j/statistics.j
rename to jl/statistics.jl
diff --git a/j/string.j b/jl/string.jl
similarity index 100%
rename from j/string.j
rename to jl/string.jl
diff --git a/j/subarray.j b/jl/subarray.jl
similarity index 100%
rename from j/subarray.j
rename to jl/subarray.jl
diff --git a/j/sysimg.j b/jl/sysimg.jl
similarity index 78%
rename from j/sysimg.j
rename to jl/sysimg.jl
index b115e5c2cb7f9..6210fa1a8ace0 100644
--- a/j/sysimg.j
+++ b/jl/sysimg.jl
@@ -1,99 +1,99 @@
 ## Load essential files and libraries
 
-include("base.j")
+include("base.jl")
 
 # core operations & types
-include("range.j")
-include("tuple.j")
-include("cell.j")
-include("expr.j")
-include("error.j")
+include("range.jl")
+include("tuple.jl")
+include("cell.jl")
+include("expr.jl")
+include("error.jl")
 
 # core numeric operations & types
-include("bool.j")
-include("number.j")
-include("int.j")
-include("promotion.j")
-include("operators.j")
-include("float.j")
-include("pointer.j")
-include("char.j")
-include("reduce.j")
-include("complex.j")
-include("rational.j")
+include("bool.jl")
+include("number.jl")
+include("int.jl")
+include("promotion.jl")
+include("operators.jl")
+include("float.jl")
+include("pointer.jl")
+include("char.jl")
+include("reduce.jl")
+include("complex.jl")
+include("rational.jl")
 
 # core data structures (used by type inference)
-include("abstractarray.j")
-include("subarray.j")
-include("array.j")
-include("intset.j")
-include("table.j")
-include("set.j")
+include("abstractarray.jl")
+include("subarray.jl")
+include("array.jl")
+include("intset.jl")
+include("table.jl")
+include("set.jl")
 
 # compiler
-include("inference.j")
+include("inference.jl")
 
 # I/O, strings & printing
-include("io.j")
+include("io.jl")
 #set_current_output_stream(make_stdout_stream()) # for error reporting
-include("string.j")
-include("ascii.j")
-include("utf8.j")
-include("regex.j")
-include("show.j")
-include("grisu.j")
-include("printf.j")
+include("string.jl")
+include("ascii.jl")
+include("utf8.jl")
+include("regex.jl")
+include("show.jl")
+include("grisu.jl")
+include("printf.jl")
 
 # system & environment
-include("libc.j")
-include("env.j")
-include("errno_h.j")
+include("libc.jl")
+include("env.jl")
+include("errno_h.jl")
 
 # concurrency and parallelism
-include("iterator.j")
-include("task.j")
-include("process.j")
-include("serialize.j")
-include("multi.j")
+include("iterator.jl")
+include("task.jl")
+include("process.jl")
+include("serialize.jl")
+include("multi.jl")
 
 # front end
-include("client.j")
+include("client.jl")
 
 # core math functions
-include("intfuncs.j")
-include("floatfuncs.j")
-include("math.j")
-include("math_libm.j")
-include("sort.j")
-include("combinatorics.j")
-include("statistics.j")
+include("intfuncs.jl")
+include("floatfuncs.jl")
+include("math.jl")
+include("math_libm.jl")
+include("sort.jl")
+include("combinatorics.jl")
+include("statistics.jl")
 
 # random number generation
-include("random.j")
+include("random.jl")
 
 # sparse matrices
-include("sparse.j")
+include("sparse.jl")
 
 # distributed arrays
-include("darray.j")
+include("darray.jl")
 
 # utilities - version, timing, help, edit
-include("version.j")
-include("util.j")
-include("datafmt.j")
+include("version.jl")
+include("util.jl")
+include("datafmt.jl")
 
 ## Load optional external libraries
 
 # linear algebra
-include("linalg.j")
-include("linalg_blas.j")
-include("linalg_lapack.j")
-include("linalg_arpack.j")
-include("linalg_suitesparse.j")
+include("linalg.jl")
+include("linalg_blas.jl")
+include("linalg_lapack.jl")
+include("linalg_arpack.jl")
+include("linalg_suitesparse.jl")
 
 # signal processing
-include("signal.j")
-include("signal_fftw.j")
+include("signal.jl")
+include("signal_fftw.jl")
 
 
 # prime method cache with some things we know we'll need right after startup
diff --git a/j/table.j b/jl/table.jl
similarity index 100%
rename from j/table.j
rename to jl/table.jl
diff --git a/j/task.j b/jl/task.jl
similarity index 100%
rename from j/task.j
rename to jl/task.jl
diff --git a/j/tuple.j b/jl/tuple.jl
similarity index 100%
rename from j/tuple.j
rename to jl/tuple.jl
diff --git a/j/utf32.j b/jl/utf32.jl
similarity index 100%
rename from j/utf32.j
rename to jl/utf32.jl
diff --git a/j/utf8.j b/jl/utf8.jl
similarity index 99%
rename from j/utf8.j
rename to jl/utf8.jl
index 951f8e5c97e54..4dbaf0889cc61 100644
--- a/j/utf8.j
+++ b/jl/utf8.jl
@@ -1,4 +1,4 @@
-## from src/boot.j:
+## from src/boot.jl:
 # type UTF8String <: String; data::Array{Uint8,1}; end
 
 ## basic UTF-8 decoding & iteration ##
diff --git a/j/util.j b/jl/util.jl
similarity index 99%
rename from j/util.j
rename to jl/util.jl
index d502b775a8e17..aa654753d476e 100644
--- a/j/util.j
+++ b/jl/util.jl
@@ -82,7 +82,7 @@ function_loc(f::Function) = function_loc(f, (Any...))
 edit(file::String) = edit(file, 1)
 function edit(file::String, line::Int)
     editor = get(ENV, "JULIA_EDITOR", "emacs")
-    issrc = file[end-1:end] == ".j"
+    issrc = file[end-2:end] == ".jl"
     if issrc
         if editor == "emacs"
             jmode = "$JULIA_HOME/contrib/julia-mode.el"
diff --git a/j/version.j b/jl/version.jl
similarity index 100%
rename from j/version.j
rename to jl/version.jl
diff --git a/src/boot.j b/src/boot.jl
similarity index 100%
rename from src/boot.j
rename to src/boot.jl
diff --git a/src/builtins.c b/src/builtins.c
index 77d69ca437fa5..762a0a52aa911 100644
--- a/src/builtins.c
+++ b/src/builtins.c
@@ -453,13 +453,13 @@ char *jl_find_file_in_path(const char *fname)
 {
     char *fpath = (char*)fname;
     int fid = open (fpath, O_RDONLY);
-    // try adding julia home, then julia_home/j/
+    // try adding julia home, then julia_home/jl/
     if (fid == -1 && julia_home && fname[0] != '/') {
         asprintf(&fpath, "%s/%s", julia_home, fname);
         fid = open (fpath, O_RDONLY);
         if (fid == -1) {
             free(fpath);
-            asprintf(&fpath, "%s/j/%s", julia_home, fname);
+            asprintf(&fpath, "%s/jl/%s", julia_home, fname);
             fid = open (fpath, O_RDONLY);
         }
     }
diff --git a/src/init.c b/src/init.c
index 87b05e049e1c9..ece4a05b25346 100644
--- a/src/init.c
+++ b/src/init.c
@@ -126,7 +126,7 @@ void julia_init(char *imageFile)
         jl_current_module = jl_base_module;
         jl_init_intrinsic_functions();
         jl_init_primitives();
-        jl_load("src/boot.j");
+        jl_load("src/boot.jl");
         jl_get_builtin_hooks();
         jl_boot_file_loaded = 1;
         jl_init_box_caches();
@@ -220,7 +220,7 @@ static jl_value_t *sysmod(char *name)
 
 jl_function_t *jl_method_missing_func=NULL;
 
-// fetch references to things defined in boot.j
+// fetch references to things defined in boot.jl
 void jl_get_builtin_hooks(void)
 {
     jl_nothing      = base("nothing");
diff --git a/test/Makefile b/test/Makefile
index 2179fff07b356..b3c74ae99df90 100644
--- a/test/Makefile
+++ b/test/Makefile
@@ -9,13 +9,13 @@ all extra unicode::
 default all extra \
 core numbers strings corelib hashing arrayops \
 sparse lapack fft arpack random unicode amos bigint::
-	$(QUIET_JULIA) ../julia ./runtests.j $@
+	$(QUIET_JULIA) ../julia ./runtests.jl $@
 
 perf:
 ifneq ($(MAKECMDGOALS),perf)
-	$(QUIET_JULIA) ../julia perf/$@.j
+	$(QUIET_JULIA) ../julia perf/$@.jl
 else
-	@../julia perf/$@.j | perl -nle '@_=split/,/; printf "%-14s %7.3f\n", $$_[1], $$_[2]'
+	@../julia perf/$@.jl | perl -nle '@_=split/,/; printf "%-14s %7.3f\n", $$_[1], $$_[2]'
 endif
 
 benchmark:
diff --git a/test/all.j b/test/all.j
deleted file mode 100644
index aa5c879feb6f1..0000000000000
--- a/test/all.j
+++ /dev/null
@@ -1,2 +0,0 @@
-load("default.j")
-load("extra.j")
diff --git a/test/all.jl b/test/all.jl
new file mode 100644
index 0000000000000..22ca0c27c2b2e
--- /dev/null
+++ b/test/all.jl
@@ -0,0 +1,2 @@
+load("default.jl")
+load("extra.jl")
diff --git a/test/amos.j b/test/amos.jl
similarity index 100%
rename from test/amos.j
rename to test/amos.jl
diff --git a/test/arpack.j b/test/arpack.jl
similarity index 100%
rename from test/arpack.j
rename to test/arpack.jl
diff --git a/test/arrayops.j b/test/arrayops.jl
similarity index 100%
rename from test/arrayops.j
rename to test/arrayops.jl
diff --git a/test/bench/hpl_par.j b/test/bench/hpl_par.jl
similarity index 100%
rename from test/bench/hpl_par.j
rename to test/bench/hpl_par.jl
diff --git a/test/bench/hpl_seq.j b/test/bench/hpl_seq.jl
similarity index 100%
rename from test/bench/hpl_seq.j
rename to test/bench/hpl_seq.jl
diff --git a/test/bigint.j b/test/bigint.jl
similarity index 97%
rename from test/bigint.j
rename to test/bigint.jl
index fef95bccc8c4a..a505aaa1ee5c1 100644
--- a/test/bigint.j
+++ b/test/bigint.jl
@@ -1,5 +1,5 @@
 
-load ("../j/bigint.j")
+load ("../jl/bigint.jl")
 a=BigInt("123456789012345678901234567890")
 b=BigInt("123456789012345678901234567891")
 
diff --git a/test/core.j b/test/core.jl
similarity index 100%
rename from test/core.j
rename to test/core.jl
diff --git a/test/corelib.j b/test/corelib.jl
similarity index 100%
rename from test/corelib.j
rename to test/corelib.jl
diff --git a/test/default.j b/test/default.jl
similarity index 100%
rename from test/default.j
rename to test/default.jl
diff --git a/test/extra.j b/test/extra.jl
similarity index 100%
rename from test/extra.j
rename to test/extra.jl
diff --git a/test/fft.j b/test/fft.jl
similarity index 100%
rename from test/fft.j
rename to test/fft.jl
diff --git a/test/functional.j b/test/functional.jl
similarity index 83%
rename from test/functional.j
rename to test/functional.jl
index 9ac2145f105f3..72bb60dbf3d55 100644
--- a/test/functional.j
+++ b/test/functional.jl
@@ -1,28 +1,28 @@
 # tests related to functional programming functions and styles
 
-# map -- array.j
+# map -- array.jl
 @assert map((x)->"$x"[end:end], [9:11]) == ["9", "0", "1"]
 # TODO: @assert map_to()
 
-# maps of tuples (formerly in test/core.j) -- tuple.j
+# maps of tuples (formerly in test/core.jl) -- tuple.jl
 @assert map((x,y)->x+y,(1,2,3),(4,5,6)) == (5,7,9)
 @assert map((x,y)->x+y,
             (100001,100002,100003),
             (100004,100005,100006)) == (200005,200007,200009)
 
-# maps of strings (character arrays) -- string.j
+# maps of strings (character arrays) -- string.jl
 @assert map((c)->char(c+1), "abcDEF") == "bcdEFG"
 
-# reduce -- reduce.j
+# reduce -- reduce.jl
 @assert reduce((x,y)->"($x+$y)", [9:11]) == "((9+10)+11)"
 @assert reduce(max, [8 6 7 5 3 0 9]) == 9
 @assert reduce(-, 1000, [1:5]) == (1000 - 1 - 2 - 3 - 4 - 5)
 
-# mapreduce -- reduce.j
+# mapreduce -- reduce.jl
 @assert mapreduce(-, -, [-10 -9 -3]) == ((10 - 9) - 3)
 @assert mapreduce((x,y)->"($x+$y)", (x)->x[1:3], ["abcd", "efgh", "01234"]) == "((abc+efg)+012)"
 
-# filter -- array.j
+# filter -- array.jl
 @assert filter(x->(x>1), [0 1 2 3 2 1 0]) == [2, 3, 2]
 # TODO: @assert_throws_error filter(x->x+1, [0 1 2 3 2 1 0]) == [2, 3, 2]
 @assert filter(x->(x>10), [0 1 2 3 2 1 0]) == []
diff --git a/test/hashing.j b/test/hashing.jl
similarity index 100%
rename from test/hashing.j
rename to test/hashing.jl
diff --git a/test/lapack.j b/test/lapack.jl
similarity index 100%
rename from test/lapack.j
rename to test/lapack.jl
diff --git a/test/numbers.j b/test/numbers.jl
similarity index 100%
rename from test/numbers.j
rename to test/numbers.jl
diff --git a/test/perf.j b/test/perf.j
deleted file mode 100644
index d33db81680627..0000000000000
--- a/test/perf.j
+++ /dev/null
@@ -1 +0,0 @@
-print_to_string(@thunk load("perf/perf.j"))
diff --git a/test/perf.jl b/test/perf.jl
new file mode 100644
index 0000000000000..8842167721f65
--- /dev/null
+++ b/test/perf.jl
@@ -0,0 +1 @@
+print_to_string(@thunk load("perf/perf.jl"))
diff --git a/test/perf/Makefile b/test/perf/Makefile
index 27b1be5fa29c3..988401a70fac2 100644
--- a/test/perf/Makefile
+++ b/test/perf/Makefile
@@ -13,7 +13,7 @@ benchmarks/c.csv: bin/perf0 bin/perf1 bin/perf2 bin/perf3
 	for t in 1 2 3 4 5; do bin/perf2; done >>$@
 	for t in 1 2 3 4 5; do bin/perf3; done >>$@
 
-benchmarks/julia.csv: perf.j
+benchmarks/julia.csv: perf.jl
 	for t in 1 2 3 4 5; do ../../julia $<; done >$@
 
 benchmarks/python.csv: perf.py
diff --git a/test/perf/perf.j b/test/perf/perf.jl
similarity index 100%
rename from test/perf/perf.j
rename to test/perf/perf.jl
diff --git a/test/perf_cat.j b/test/perf_cat.jl
similarity index 100%
rename from test/perf_cat.j
rename to test/perf_cat.jl
diff --git a/test/random.j b/test/random.jl
similarity index 100%
rename from test/random.j
rename to test/random.jl
diff --git a/test/runtests.j b/test/runtests.jl
similarity index 97%
rename from test/runtests.j
rename to test/runtests.jl
index 424b95eb55444..8a153a29acb3c 100644
--- a/test/runtests.j
+++ b/test/runtests.jl
@@ -1,6 +1,6 @@
 function runtests(name)
     println("     \033[1m*\033[0m \033[31m$(name)\033[0m")
-    load("$name.j")
+    load("$name.jl")
 end
 
 function check_approx_eq(va, vb, astr, bstr)
diff --git a/test/sparse.j b/test/sparse.jl
similarity index 100%
rename from test/sparse.j
rename to test/sparse.jl
diff --git a/test/strings.j b/test/strings.jl
similarity index 100%
rename from test/strings.j
rename to test/strings.jl
diff --git a/test/unicode.j b/test/unicode.jl
similarity index 100%
rename from test/unicode.j
rename to test/unicode.jl
diff --git a/ui/webserver/julia_web.j b/ui/webserver/julia_web.jl
similarity index 100%
rename from ui/webserver/julia_web.j
rename to ui/webserver/julia_web.jl
diff --git a/ui/webserver/julia_web_base.j b/ui/webserver/julia_web_base.jl
similarity index 99%
rename from ui/webserver/julia_web_base.j
rename to ui/webserver/julia_web_base.jl
index 97dbcb2d350dc..af88ff9a12d10 100755
--- a/ui/webserver/julia_web_base.j
+++ b/ui/webserver/julia_web_base.jl
@@ -91,7 +91,7 @@ end
 ###########################################
 
 # load the special functions available to the web repl
-load("./ui/webserver/julia_web.j")
+load("./ui/webserver/julia_web.jl")
 
 ###########################################
 # input event handler
diff --git a/ui/webserver/webserver.cpp b/ui/webserver/webserver.cpp
index 57d5fa5d40bd1..f089d97f7bf51 100644
--- a/ui/webserver/webserver.cpp
+++ b/ui/webserver/webserver.cpp
@@ -44,7 +44,7 @@ template <class T> T from_string(const std::string& t)
 class message
 {
 public:
-    // see ui/webserver/julia_web_base.j for documentation
+    // see ui/webserver/julia_web_base.jl for documentation
     uint8_t type;
     vector<string> args;
 };
@@ -629,7 +629,7 @@ string create_session(bool idle)
         close(session_data.julia_out[1]);
 
         // acutally spawn julia instance
-        execl("./julia", "julia", "./ui/webserver/julia_web_base.j", (char*)0);
+        execl("./julia", "julia", "./ui/webserver/julia_web_base.jl", (char*)0);
 
         // if exec failed, terminate with an error
         exit(1);