diff --git a/data/scripts/debug.inc b/data/scripts/debug.inc
index 72ace2512ab3..3e482c839104 100644
--- a/data/scripts/debug.inc
+++ b/data/scripts/debug.inc
@@ -206,4 +206,13 @@ DebugText_DaycareOnePokemon:
 DebugText_DaycarePokemonNotCompatible:
 	.string "Your Pokémon at Daycare can't\nhave babies together!$"
 
+Debug_ShowExpansionVersion::
+	callnative BufferExpansionVersion
+	msgbox Debug_ExpansionVersion, MSGBOX_DEFAULT
+	release
+	end
+
+Debug_ExpansionVersion:
+	.string "pokeemerald-expansion {STR_VAR_1}$"
+
 .endif
diff --git a/include/constants/expansion.h b/include/constants/expansion.h
new file mode 100644
index 000000000000..872e5bbd3414
--- /dev/null
+++ b/include/constants/expansion.h
@@ -0,0 +1,12 @@
+#ifndef GUARD_CONSTANTS_EXPANSION_H
+#define GUARD_CONSTANTS_EXPANSION_H
+
+#define EXPANSION_VERSION_MAJOR 1
+#define EXPANSION_VERSION_MINOR 7
+#define EXPANSION_VERSION_PATCH 0
+
+// FALSE if this this version of Expansion is not a tagged commit, i.e.
+// it contains unreleased changes.
+#define EXPANSION_TAGGED_RELEASE FALSE
+
+#endif
diff --git a/ld_script.txt b/ld_script.txt
index 27b340f49099..6b7d115b2295 100644
--- a/ld_script.txt
+++ b/ld_script.txt
@@ -52,6 +52,7 @@ SECTIONS {
     {
         src/rom_header.o(.text);
         src/rom_header_gf.o(.text.*);
+        src/rom_header_rhh.o(.text.*);
         src/crt0.o(.text);
         src/main.o(.text);
         gflib/malloc.o(.text);
diff --git a/ld_script_modern.txt b/ld_script_modern.txt
index ab68976661b1..7a14cfa52c3f 100644
--- a/ld_script_modern.txt
+++ b/ld_script_modern.txt
@@ -51,6 +51,7 @@ SECTIONS {
     {
         src/rom_header.o(.text*);
         src/rom_header_gf.o(.text.*);
+        src/rom_header_rhh.o(.text.*);
         src/crt0.o(.text);
         src/main.o(.text);
         gflib/*.o(.text*);
diff --git a/ld_script_test.txt b/ld_script_test.txt
index c7e19d7189d9..447d7a2b877a 100644
--- a/ld_script_test.txt
+++ b/ld_script_test.txt
@@ -62,6 +62,7 @@ SECTIONS {
     {
         src/rom_header.o(.text);
         src/rom_header_gf.o(.text.*);
+        src/rom_header_rhh.o(.text.*);
         src/*.o(.text);
         gflib/*.o(.text);
     } =0
diff --git a/src/debug.c b/src/debug.c
index 822d1bb4723a..8489a265c027 100644
--- a/src/debug.c
+++ b/src/debug.c
@@ -55,6 +55,7 @@
 #include "constants/battle_ai.h"
 #include "constants/battle_frontier.h"
 #include "constants/coins.h"
+#include "constants/expansion.h"
 #include "constants/flags.h"
 #include "constants/items.h"
 #include "constants/map_groups.h"
@@ -97,6 +98,7 @@ enum UtilMenu
     DEBUG_UTIL_MENU_ITEM_CLEAR_BOXES,
     DEBUG_UTIL_MENU_ITEM_CHEAT,
     DEBUG_UTIL_MENU_ITEM_HATCH_AN_EGG,
+    DEBUG_UTIL_MENU_ITEM_EXPANSION_VER,
 };
 
 enum ScriptMenu
@@ -339,6 +341,7 @@ static void DebugAction_Util_Player_Id(u8 taskId);
 static void DebugAction_Util_Clear_Boxes(u8 taskId);
 static void DebugAction_Util_CheatStart(u8 taskId);
 static void DebugAction_Util_HatchAnEgg(u8 taskId);
+static void DebugAction_Util_ExpansionVersion(u8 taskId);
 
 static void DebugAction_FlagsVars_Flags(u8 taskId);
 static void DebugAction_FlagsVars_FlagsSelect(u8 taskId);
@@ -418,6 +421,7 @@ extern const u8 PlayersHouse_2F_EventScript_CheckWallClock[];
 extern const u8 Debug_CheckSaveBlock[];
 extern const u8 Debug_CheckROMSpace[];
 extern const u8 Debug_BoxFilledMessage[];
+extern const u8 Debug_ShowExpansionVersion[];
 
 #include "data/map_group_count.h"
 
@@ -471,6 +475,7 @@ static const u8 sDebugText_Util_Player_Id[] =                _("New Trainer Id")
 static const u8 sDebugText_Util_Clear_Boxes[] =              _("Clear Storage Boxes");
 static const u8 sDebugText_Util_CheatStart[] =               _("CHEAT Start");
 static const u8 sDebugText_Util_HatchAnEgg[] =               _("Hatch an Egg");
+static const u8 sDebugText_Util_ExpansionVersion[] =         _("Expansion Version");
 // Flags/Vars Menu
 static const u8 sDebugText_FlagsVars_Flags[] =                  _("Set Flag XYZ…{CLEAR_TO 110}{RIGHT_ARROW}");
 static const u8 sDebugText_FlagsVars_Flag[] =                   _("Flag: {STR_VAR_1}{CLEAR_TO 90}\n{STR_VAR_2}{CLEAR_TO 90}\n{STR_VAR_3}");
@@ -637,6 +642,7 @@ static const struct ListMenuItem sDebugMenu_Items_Utilities[] =
     [DEBUG_UTIL_MENU_ITEM_CLEAR_BOXES]    = {sDebugText_Util_Clear_Boxes,    DEBUG_UTIL_MENU_ITEM_CLEAR_BOXES},
     [DEBUG_UTIL_MENU_ITEM_CHEAT]          = {sDebugText_Util_CheatStart,     DEBUG_UTIL_MENU_ITEM_CHEAT},
     [DEBUG_UTIL_MENU_ITEM_HATCH_AN_EGG]   = {sDebugText_Util_HatchAnEgg,     DEBUG_UTIL_MENU_ITEM_HATCH_AN_EGG},
+    [DEBUG_UTIL_MENU_ITEM_EXPANSION_VER]  = {sDebugText_Util_ExpansionVersion,DEBUG_UTIL_MENU_ITEM_EXPANSION_VER},
 };
 
 static const struct ListMenuItem sDebugMenu_Items_Scripts[] =
@@ -780,6 +786,7 @@ static void (*const sDebugMenu_Actions_Utilities[])(u8) =
     [DEBUG_UTIL_MENU_ITEM_CLEAR_BOXES]    = DebugAction_Util_Clear_Boxes,
     [DEBUG_UTIL_MENU_ITEM_CHEAT]          = DebugAction_Util_CheatStart,
     [DEBUG_UTIL_MENU_ITEM_HATCH_AN_EGG]   = DebugAction_Util_HatchAnEgg,
+    [DEBUG_UTIL_MENU_ITEM_EXPANSION_VER]  = DebugAction_Util_ExpansionVersion,
 };
 
 static void (*const sDebugMenu_Actions_Scripts[])(u8) =
@@ -2122,6 +2129,30 @@ static void DebugAction_Util_HatchAnEgg(u8 taskId)
     Debug_DestroyMenu_Full_Script(taskId, Debug_HatchAnEgg);
 }
 
+static void DebugAction_Util_ExpansionVersion(u8 taskId)
+{
+    Debug_DestroyMenu_Full(taskId);
+    LockPlayerFieldControls();
+    ScriptContext_SetupScript(Debug_ShowExpansionVersion);
+}
+
+void BufferExpansionVersion(struct ScriptContext *ctx)
+{
+    static const u8 sText_Released[] = _("\nRelease Build");
+    static const u8 sText_Unreleased[] = _("\nDevelopment Build");
+    u8 *string = gStringVar1;
+    *string++ = CHAR_v;
+    string = ConvertIntToDecimalStringN(string, EXPANSION_VERSION_MAJOR, STR_CONV_MODE_LEFT_ALIGN, 3);
+    *string++ = CHAR_PERIOD;
+    string = ConvertIntToDecimalStringN(string, EXPANSION_VERSION_MINOR, STR_CONV_MODE_LEFT_ALIGN, 3);
+    *string++ = CHAR_PERIOD;
+    string = ConvertIntToDecimalStringN(string, EXPANSION_VERSION_PATCH, STR_CONV_MODE_LEFT_ALIGN, 3);
+    if (EXPANSION_TAGGED_RELEASE)
+        string = StringCopy(string, sText_Released);
+    else
+        string = StringCopy(string, sText_Unreleased);
+}
+
 // *******************************
 // Actions Scripts
 static void DebugAction_Util_Script_1(u8 taskId)
diff --git a/src/rom_header_rhh.c b/src/rom_header_rhh.c
new file mode 100644
index 000000000000..2e141670a744
--- /dev/null
+++ b/src/rom_header_rhh.c
@@ -0,0 +1,26 @@
+#include "global.h"
+#include "constants/expansion.h"
+
+// Similar to the GF ROM header, this struct allows external programs to
+// detect details about Expansion.
+// For this structure to be useful we have to maintain backwards binary
+// compatibility. This means that we should only ever append data to the
+// end. If there are any structs as members then those structs should
+// not be modified after being introduced.
+struct RHHRomHeader
+{
+    /*0x00*/ char rhh_magic[6]; // 'RHHEXP'. Useful to locate the header if it shifts.
+    /*0x06*/ u8 expansionVersionMajor;
+    /*0x07*/ u8 expansionVersionMinor;
+    /*0x08*/ u8 expansionVersionPatch;
+    /*0x09*/ u8 expansionVersionFlags;
+};
+
+static const struct RHHRomHeader sRHHRomHeader =
+{
+    .rhh_magic = { 'R', 'H', 'H', 'E', 'X', 'P' },
+    .expansionVersionMajor = EXPANSION_VERSION_MAJOR,
+    .expansionVersionMinor = EXPANSION_VERSION_MINOR,
+    .expansionVersionPatch = EXPANSION_VERSION_PATCH,
+    .expansionVersionFlags = (EXPANSION_TAGGED_RELEASE << 0),
+};