diff --git a/Package.swift b/Package.swift
index d84cbf7d3..b52483ce8 100644
--- a/Package.swift
+++ b/Package.swift
@@ -395,14 +395,14 @@ extension Array where Element == PackageDescription.SwiftSetting {
 
       .define("SWT_TARGET_OS_APPLE", .whenApple()),
 
-      .define("SWT_NO_EXIT_TESTS", .whenEmbedded(or: .when(platforms: [.iOS, .watchOS, .tvOS, .visionOS, .wasi, .android]))),
-      .define("SWT_NO_PROCESS_SPAWNING", .whenEmbedded(or: .when(platforms: [.iOS, .watchOS, .tvOS, .visionOS, .wasi, .android]))),
+      .define("SWT_NO_EXIT_TESTS", .whenEmbedded(or: .when(platforms: [.iOS, .watchOS, .tvOS, .visionOS, .wasi, .custom("emscripten"), .android]))),
+      .define("SWT_NO_PROCESS_SPAWNING", .whenEmbedded(or: .when(platforms: [.iOS, .watchOS, .tvOS, .visionOS, .wasi, .custom("emscripten"), .android]))),
       .define("SWT_NO_SNAPSHOT_TYPES", .whenEmbedded(or: .whenApple(false))),
-      .define("SWT_NO_DYNAMIC_LINKING", .whenEmbedded(or: .when(platforms: [.wasi]))),
-      .define("SWT_NO_PIPES", .whenEmbedded(or: .when(platforms: [.wasi]))),
+      .define("SWT_NO_DYNAMIC_LINKING", .whenEmbedded(or: .when(platforms: [.wasi, .custom("emscripten")]))),
+      .define("SWT_NO_PIPES", .whenEmbedded(or: .when(platforms: [.wasi, .custom("emscripten")]))),
       .define("SWT_NO_FOUNDATION_FILE_COORDINATION", .whenEmbedded(or: .whenApple(false))),
-      .define("SWT_NO_IMAGE_ATTACHMENTS", .whenEmbedded(or: .when(platforms: [.linux, .custom("freebsd"), .openbsd, .wasi, .android]))),
-      .define("SWT_NO_FILE_CLONING", .whenEmbedded(or: .when(platforms: [.openbsd, .wasi, .android]))),
+      .define("SWT_NO_IMAGE_ATTACHMENTS", .whenEmbedded(or: .when(platforms: [.linux, .custom("freebsd"), .openbsd, .wasi, .custom("emscripten"), .android]))),
+      .define("SWT_NO_FILE_CLONING", .whenEmbedded(or: .when(platforms: [.openbsd, .wasi, .custom("emscripten"), .android]))),
 
       .define("SWT_NO_LEGACY_TEST_DISCOVERY", .whenEmbedded()),
       .define("SWT_NO_LIBDISPATCH", .whenEmbedded()),
@@ -478,14 +478,14 @@ extension Array where Element == PackageDescription.CXXSetting {
     var result = Self()
 
     result += [
-      .define("SWT_NO_EXIT_TESTS", .whenEmbedded(or: .when(platforms: [.iOS, .watchOS, .tvOS, .visionOS, .wasi, .android]))),
-      .define("SWT_NO_PROCESS_SPAWNING", .whenEmbedded(or: .when(platforms: [.iOS, .watchOS, .tvOS, .visionOS, .wasi, .android]))),
+      .define("SWT_NO_EXIT_TESTS", .whenEmbedded(or: .when(platforms: [.iOS, .watchOS, .tvOS, .visionOS, .wasi, .custom("emscripten"), .android]))),
+      .define("SWT_NO_PROCESS_SPAWNING", .whenEmbedded(or: .when(platforms: [.iOS, .watchOS, .tvOS, .visionOS, .wasi, .custom("emscripten"), .android]))),
       .define("SWT_NO_SNAPSHOT_TYPES", .whenEmbedded(or: .whenApple(false))),
-      .define("SWT_NO_DYNAMIC_LINKING", .whenEmbedded(or: .when(platforms: [.wasi]))),
-      .define("SWT_NO_PIPES", .whenEmbedded(or: .when(platforms: [.wasi]))),
+      .define("SWT_NO_DYNAMIC_LINKING", .whenEmbedded(or: .when(platforms: [.wasi, .custom("emscripten")]))),
+      .define("SWT_NO_PIPES", .whenEmbedded(or: .when(platforms: [.wasi, .custom("emscripten")]))),
       .define("SWT_NO_FOUNDATION_FILE_COORDINATION", .whenEmbedded(or: .whenApple(false))),
-      .define("SWT_NO_IMAGE_ATTACHMENTS", .whenEmbedded(or: .when(platforms: [.linux, .custom("freebsd"), .openbsd, .wasi, .android]))),
-      .define("SWT_NO_FILE_CLONING", .whenEmbedded(or: .when(platforms: [.openbsd, .wasi, .android]))),
+      .define("SWT_NO_IMAGE_ATTACHMENTS", .whenEmbedded(or: .when(platforms: [.linux, .custom("freebsd"), .openbsd, .wasi, .custom("emscripten"), .android]))),
+      .define("SWT_NO_FILE_CLONING", .whenEmbedded(or: .when(platforms: [.openbsd, .wasi, .custom("emscripten"), .android]))),
 
       .define("SWT_NO_LEGACY_TEST_DISCOVERY", .whenEmbedded()),
       .define("SWT_NO_LIBDISPATCH", .whenEmbedded()),
diff --git a/Sources/Testing/ABI/EntryPoints/EntryPoint.swift b/Sources/Testing/ABI/EntryPoints/EntryPoint.swift
index 64cef7759..5a2b6a5a0 100644
--- a/Sources/Testing/ABI/EntryPoints/EntryPoint.swift
+++ b/Sources/Testing/ABI/EntryPoints/EntryPoint.swift
@@ -798,7 +798,7 @@ extension Event.ConsoleOutputRecorder.Options {
     // Windows does not set the "TERM" variable, so assume it supports 16-color
     // ANSI escape codes.
     true
-#elseif os(WASI)
+#elseif os(WASI) || os(Emscripten)
     // The "Terminal" under WASI can be assumed to be the browser's JavaScript
     // console, which we don't expect supports color escape codes.
     false
@@ -820,7 +820,7 @@ extension Event.ConsoleOutputRecorder.Options {
     // Windows does not set the "TERM" variable, so assume it supports 256-color
     // ANSI escape codes.
     true
-#elseif os(WASI)
+#elseif os(WASI) || os(Emscripten)
     // The "Terminal" under WASI can be assumed to be the browser's JavaScript
     // console, which we don't expect supports color escape codes.
     false
@@ -842,7 +842,7 @@ extension Event.ConsoleOutputRecorder.Options {
     // Windows does not set the "COLORTERM" variable, so assume it supports
     // true-color ANSI escape codes. SEE: https://github.com/microsoft/terminal/issues/11057
     true
-#elseif os(WASI)
+#elseif os(WASI) || os(Emscripten)
     // The "Terminal" under WASI can be assumed to be the browser's JavaScript
     // console, which we don't expect supports color escape codes.
     false
diff --git a/Sources/Testing/ABI/EntryPoints/SwiftPMEntryPoint.swift b/Sources/Testing/ABI/EntryPoints/SwiftPMEntryPoint.swift
index 3c72e9f20..26091d166 100644
--- a/Sources/Testing/ABI/EntryPoints/SwiftPMEntryPoint.swift
+++ b/Sources/Testing/ABI/EntryPoints/SwiftPMEntryPoint.swift
@@ -24,7 +24,7 @@ private import _TestingInternals
 ///
 /// This constant is not part of the public interface of the testing library.
 var EXIT_NO_TESTS_FOUND: CInt {
-#if SWT_TARGET_OS_APPLE || os(Linux) || os(FreeBSD) || os(OpenBSD) || os(Android) || os(WASI)
+#if SWT_TARGET_OS_APPLE || os(Linux) || os(FreeBSD) || os(OpenBSD) || os(Android) || os(WASI) || os(Emscripten)
   EX_UNAVAILABLE
 #elseif os(Windows)
   CInt(ERROR_NOT_FOUND)
diff --git a/Sources/Testing/CMakeLists.txt b/Sources/Testing/CMakeLists.txt
index 43a67f0ac..25bfe465f 100644
--- a/Sources/Testing/CMakeLists.txt
+++ b/Sources/Testing/CMakeLists.txt
@@ -133,12 +133,14 @@ target_link_libraries(Testing PRIVATE
   _TestingInternals
   _TestingInterop)
 if(NOT APPLE)
-  if(NOT CMAKE_SYSTEM_NAME STREQUAL WASI)
+  if(NOT CMAKE_SYSTEM_NAME STREQUAL WASI AND NOT CMAKE_SYSTEM_NAME STREQUAL Emscripten)
     target_link_libraries(Testing PUBLIC
       dispatch)
   endif()
-  target_link_libraries(Testing PUBLIC
-    Foundation)
+  if(NOT CMAKE_SYSTEM_NAME STREQUAL Emscripten)
+    target_link_libraries(Testing PUBLIC
+      Foundation)
+  endif()
   if (CMAKE_SYSTEM_NAME STREQUAL "FreeBSD" OR
       CMAKE_SYSTEM_NAME STREQUAL "OpenBSD")
     target_link_libraries(Testing PUBLIC execinfo)
diff --git a/Sources/Testing/ExitTests/ExitStatus.swift b/Sources/Testing/ExitTests/ExitStatus.swift
index f028e3891..68648f5bb 100644
--- a/Sources/Testing/ExitTests/ExitStatus.swift
+++ b/Sources/Testing/ExitTests/ExitStatus.swift
@@ -141,7 +141,7 @@ extension ExitStatus: CustomStringConvertible {
         .flatMap(String.init(validatingCString:))
         .map { "SIG\($0)" }
 #endif
-#elseif os(Windows) || os(WASI)
+#elseif os(Windows) || os(WASI) || os(Emscripten)
       // These platforms do not have API to get the programmatic name of a
       // signal constant.
 #else
diff --git a/Sources/Testing/SourceAttribution/Backtrace.swift b/Sources/Testing/SourceAttribution/Backtrace.swift
index 3c6e412be..98f32a7cf 100644
--- a/Sources/Testing/SourceAttribution/Backtrace.swift
+++ b/Sources/Testing/SourceAttribution/Backtrace.swift
@@ -85,7 +85,7 @@ public struct Backtrace: Sendable {
       initializedCount = .init(clamping: backtrace(addresses.baseAddress!, .init(clamping: addresses.count)))
 #elseif os(Windows)
       initializedCount = Int(clamping: RtlCaptureStackBackTrace(0, ULONG(clamping: addresses.count), addresses.baseAddress!, nil))
-#elseif os(WASI)
+#elseif os(WASI) || os(Emscripten)
       // SEE: https://github.com/WebAssembly/WASI/issues/159
       // SEE: https://github.com/swiftlang/swift/pull/31693
 #else
diff --git a/Sources/Testing/Support/Additions/CommandLineAdditions.swift b/Sources/Testing/Support/Additions/CommandLineAdditions.swift
index 6f307acfb..ea21cf500 100644
--- a/Sources/Testing/Support/Additions/CommandLineAdditions.swift
+++ b/Sources/Testing/Support/Additions/CommandLineAdditions.swift
@@ -107,7 +107,7 @@ extension CommandLine {
         }
       }
       return result!
-#elseif os(WASI)
+#elseif os(WASI) || os(Emscripten)
       // WASI does not really have the concept of a file system path to the main
       // executable, so simply return the first argument--presumably the program
       // name, but as you know this is not guaranteed by the C standard!
diff --git a/Sources/Testing/Support/Environment.swift b/Sources/Testing/Support/Environment.swift
index 5280d3954..b2f2f2caf 100644
--- a/Sources/Testing/Support/Environment.swift
+++ b/Sources/Testing/Support/Environment.swift
@@ -46,7 +46,7 @@ package enum Environment {
     }
   }
 
-#if SWT_TARGET_OS_APPLE || os(Linux) || os(FreeBSD) || os(OpenBSD) || os(Android) || os(WASI)
+#if SWT_TARGET_OS_APPLE || os(Linux) || os(FreeBSD) || os(OpenBSD) || os(Android) || os(WASI) || os(Emscripten)
   /// Get all environment variables from a POSIX environment block.
   ///
   /// - Parameters:
@@ -107,7 +107,7 @@ package enum Environment {
     }
 #endif
     return _get(fromEnviron: _NSGetEnviron()!.pointee!)
-#elseif os(Linux) || os(FreeBSD) || os(OpenBSD) || os(Android)
+#elseif os(Linux) || os(FreeBSD) || os(OpenBSD) || os(Android) || os(Emscripten)
     _get(fromEnviron: swt_environ())
 #elseif os(WASI)
     _get(fromEnviron: __wasilibc_get_environ())
@@ -174,7 +174,7 @@ package enum Environment {
       }
       return nil
     }
-#elseif SWT_TARGET_OS_APPLE || os(Linux) || os(FreeBSD) || os(OpenBSD) || os(Android) || os(WASI)
+#elseif SWT_TARGET_OS_APPLE || os(Linux) || os(FreeBSD) || os(OpenBSD) || os(Android) || os(WASI) || os(Emscripten)
     getenv(name).flatMap { String(validatingCString: $0) }
 #elseif os(Windows)
     name.withCString(encodedAs: UTF16.self) { name in
@@ -258,7 +258,7 @@ extension Environment {
       environment[name] = value
     }
     return true
-#elseif SWT_TARGET_OS_APPLE || os(Linux) || os(FreeBSD) || os(OpenBSD) || os(Android) || os(WASI)
+#elseif SWT_TARGET_OS_APPLE || os(Linux) || os(FreeBSD) || os(OpenBSD) || os(Android) || os(WASI) || os(Emscripten)
     if let value {
       return 0 == setenv(name, value, 1)
     }
diff --git a/Sources/Testing/Support/FileHandle.swift b/Sources/Testing/Support/FileHandle.swift
index 338fd064c..111080fe6 100644
--- a/Sources/Testing/Support/FileHandle.swift
+++ b/Sources/Testing/Support/FileHandle.swift
@@ -309,7 +309,7 @@ struct FileHandle: ~Copyable, Sendable {
   /// descriptor, `nil` is passed to `body`.
   borrowing func withUnsafePOSIXFileDescriptor<R>(_ body: (CInt?) throws -> R) rethrows -> R {
     try withUnsafeCFILEHandle { handle in
-#if SWT_TARGET_OS_APPLE || os(Linux) || os(FreeBSD) || os(OpenBSD) || os(Android) || os(WASI)
+#if SWT_TARGET_OS_APPLE || os(Linux) || os(FreeBSD) || os(OpenBSD) || os(Android) || os(WASI) || os(Emscripten)
       let fd = fileno(handle)
 #elseif os(Windows)
       let fd = _fileno(handle)
@@ -368,7 +368,7 @@ struct FileHandle: ~Copyable, Sendable {
   /// other threads.
   borrowing func withLock<R>(_ body: () throws -> R) rethrows -> R {
     try withUnsafeCFILEHandle { handle in
-#if SWT_TARGET_OS_APPLE || os(Linux) || os(FreeBSD) || os(OpenBSD) || os(Android)
+#if SWT_TARGET_OS_APPLE || os(Linux) || os(FreeBSD) || os(OpenBSD) || os(Android) || os(Emscripten)
       flockfile(handle)
       defer {
         funlockfile(handle)
@@ -403,7 +403,7 @@ extension FileHandle {
     // If possible, reserve enough space in the resulting buffer to contain
     // the contents of the file being read.
     var size: Int?
-#if SWT_TARGET_OS_APPLE || os(Linux) || os(FreeBSD) || os(OpenBSD) || os(Android) || os(WASI)
+#if SWT_TARGET_OS_APPLE || os(Linux) || os(FreeBSD) || os(OpenBSD) || os(Android) || os(WASI) || os(Emscripten)
     withUnsafePOSIXFileDescriptor { fd in
       var s = stat()
       if let fd, 0 == fstat(fd, &s) {
@@ -667,7 +667,7 @@ extension FileHandle {
 extension FileHandle {
   /// Is this file handle a TTY or PTY?
   var isTTY: Bool {
-#if SWT_TARGET_OS_APPLE || os(Linux) || os(FreeBSD) || os(OpenBSD) || os(Android) || os(WASI)
+#if SWT_TARGET_OS_APPLE || os(Linux) || os(FreeBSD) || os(OpenBSD) || os(Android) || os(WASI) || os(Emscripten)
     // If stderr is a TTY and TERM is set, that's good enough for us.
     withUnsafePOSIXFileDescriptor { fd in
       if let fd, 0 != isatty(fd), let term = Environment.variable(named: "TERM"), !term.isEmpty {
@@ -769,7 +769,7 @@ func fileExists(atPath path: String) -> Bool {
 ///   resolved, the resulting string may differ slightly but refers to the same
 ///   file system object. If the path could not be resolved, returns `nil`.
 func canonicalizePath(_ path: String) -> String? {
-#if SWT_TARGET_OS_APPLE || os(Linux) || os(FreeBSD) || os(OpenBSD) || os(Android) || os(WASI)
+#if SWT_TARGET_OS_APPLE || os(Linux) || os(FreeBSD) || os(OpenBSD) || os(Android) || os(WASI) || os(Emscripten)
   path.withCString { path in
     if let resolvedCPath = realpath(path, nil) {
       defer {
diff --git a/Sources/Testing/Support/Serializer.swift b/Sources/Testing/Support/Serializer.swift
index 0d252acd7..8ef87b8db 100644
--- a/Sources/Testing/Support/Serializer.swift
+++ b/Sources/Testing/Support/Serializer.swift
@@ -20,7 +20,7 @@ private var _cpuCoreCount: Int? {
   var siInfo = SYSTEM_INFO()
   GetSystemInfo(&siInfo)
   return Int(siInfo.dwNumberOfProcessors)
-#elseif os(WASI)
+#elseif os(WASI) || os(Emscripten)
   return 1
 #else
 #warning("Platform-specific implementation missing: CPU core count unavailable")
diff --git a/Sources/Testing/Support/Versions.swift b/Sources/Testing/Support/Versions.swift
index 710a28dcb..423896982 100644
--- a/Sources/Testing/Support/Versions.swift
+++ b/Sources/Testing/Support/Versions.swift
@@ -88,9 +88,10 @@ let operatingSystemVersion: String = {
       return result
     }
   }
-#elseif os(WASI)
+#elseif os(WASI) || os(Emscripten)
   // WASI does not have an API to get the current WASI or Wasm version.
   // wasi-libc does have uname(3), but it's stubbed out.
+  // Emscripten's uname(3) is similarly limited.
 #else
 #warning("Platform-specific implementation missing: OS version unavailable")
 #endif
diff --git a/Sources/Testing/Traits/Tags/Tag.Color+Loading.swift b/Sources/Testing/Traits/Tags/Tag.Color+Loading.swift
index 2ab35b107..52b83f359 100644
--- a/Sources/Testing/Traits/Tags/Tag.Color+Loading.swift
+++ b/Sources/Testing/Traits/Tags/Tag.Color+Loading.swift
@@ -70,7 +70,7 @@ var swiftTestingDirectoryPath: String? {
   if let appDataDirectoryPath = _appDataDirectoryPath {
     return appendPathComponent(swiftTestingDirectoryName, to: appDataDirectoryPath)
   }
-#elseif os(WASI)
+#elseif os(WASI) || os(Emscripten)
   // WASI does not support the concept of a home directory.
 #else
 #warning("Platform-specific implementation missing: .swift-testing directory location unavailable")
diff --git a/Sources/_TestDiscovery/SectionBounds.swift b/Sources/_TestDiscovery/SectionBounds.swift
index 6c5ab63bb..1443a4974 100644
--- a/Sources/_TestDiscovery/SectionBounds.swift
+++ b/Sources/_TestDiscovery/SectionBounds.swift
@@ -346,7 +346,7 @@ private struct _SectionBound: Sendable, ~Copyable {
 @_silgen_name(raw: "section$start$__TEXT$__swift5_types") private nonisolated(unsafe) var _typeMetadataSectionBegin: _SectionBound
 @_silgen_name(raw: "section$end$__TEXT$__swift5_types") private nonisolated(unsafe) var _typeMetadataSectionEnd: _SectionBound
 #endif
-#elseif os(Linux) || os(FreeBSD) || os(OpenBSD) || os(Android) || os(WASI)
+#elseif os(Linux) || os(FreeBSD) || os(OpenBSD) || os(Android) || os(WASI) || os(Emscripten)
 @_silgen_name(raw: "__start_swift5_tests") private nonisolated(unsafe) var _testContentSectionBegin: _SectionBound
 @_silgen_name(raw: "__stop_swift5_tests") private nonisolated(unsafe) var _testContentSectionEnd: _SectionBound
 #if !SWT_NO_LEGACY_TEST_DISCOVERY
diff --git a/Sources/_TestingInternals/include/Stubs.h b/Sources/_TestingInternals/include/Stubs.h
index 788db76ae..d7f4fa2ef 100644
--- a/Sources/_TestingInternals/include/Stubs.h
+++ b/Sources/_TestingInternals/include/Stubs.h
@@ -139,7 +139,7 @@ static const IMAGE_SECTION_HEADER *_Null_unspecified swt_IMAGE_FIRST_SECTION(con
 }
 #endif
 
-#if defined(__linux__) || defined(__FreeBSD__) || defined(__OpenBSD__) || defined(__ANDROID__)
+#if defined(__linux__) || defined(__FreeBSD__) || defined(__OpenBSD__) || defined(__ANDROID__) || defined(__EMSCRIPTEN__)
 /// The environment block.
 ///
 /// By POSIX convention, the environment block variable is declared in client
diff --git a/cmake/modules/shared/CompilerSettings.cmake b/cmake/modules/shared/CompilerSettings.cmake
index cb81e0e4a..3c575ed11 100644
--- a/cmake/modules/shared/CompilerSettings.cmake
+++ b/cmake/modules/shared/CompilerSettings.cmake
@@ -27,11 +27,11 @@ add_compile_options(
 if(APPLE)
   add_compile_definitions("SWT_TARGET_OS_APPLE")
 endif()
-set(SWT_NO_EXIT_TESTS_LIST "iOS" "watchOS" "tvOS" "visionOS" "WASI" "Android")
+set(SWT_NO_EXIT_TESTS_LIST "iOS" "watchOS" "tvOS" "visionOS" "WASI" "Emscripten" "Android")
 if(CMAKE_SYSTEM_NAME IN_LIST SWT_NO_EXIT_TESTS_LIST)
   add_compile_definitions("SWT_NO_EXIT_TESTS")
 endif()
-set(SWT_NO_PROCESS_SPAWNING_LIST "iOS" "watchOS" "tvOS" "visionOS" "WASI" "Android")
+set(SWT_NO_PROCESS_SPAWNING_LIST "iOS" "watchOS" "tvOS" "visionOS" "WASI" "Emscripten" "Android")
 if(CMAKE_SYSTEM_NAME IN_LIST SWT_NO_PROCESS_SPAWNING_LIST)
   add_compile_definitions("SWT_NO_PROCESS_SPAWNING")
 endif()
@@ -39,14 +39,14 @@ if(NOT APPLE)
   add_compile_definitions("SWT_NO_SNAPSHOT_TYPES")
   add_compile_definitions("SWT_NO_FOUNDATION_FILE_COORDINATION")
 endif()
-if(CMAKE_SYSTEM_NAME STREQUAL "WASI")
+if(CMAKE_SYSTEM_NAME STREQUAL "WASI" OR CMAKE_SYSTEM_NAME STREQUAL "Emscripten")
   add_compile_definitions("SWT_NO_DYNAMIC_LINKING")
   add_compile_definitions("SWT_NO_PIPES")
 endif()
 if (NOT (APPLE OR CMAKE_SYSTEM_NAME STREQUAL "Windows"))
   add_compile_definitions("SWT_NO_IMAGE_ATTACHMENTS")
 endif()
-set(SWT_NO_FILE_CLONING_LIST "OpenBSD" "WASI" "Android")
+set(SWT_NO_FILE_CLONING_LIST "OpenBSD" "WASI" "Emscripten" "Android")
 if(CMAKE_SYSTEM_NAME IN_LIST SWT_NO_FILE_CLONING_LIST)
   add_compile_definitions("SWT_NO_FILE_CLONING")
 endif()