diff --git a/Sources/CSystem/include/CSystemWASI.h b/Sources/CSystem/include/CSystemWASI.h
new file mode 100644
index 00000000..9877853e
--- /dev/null
+++ b/Sources/CSystem/include/CSystemWASI.h
@@ -0,0 +1,31 @@
+/*
+ This source file is part of the Swift System open source project
+
+ Copyright (c) 2024 Apple Inc. and the Swift System project authors
+ Licensed under Apache License v2.0 with Runtime Library Exception
+
+ See https://swift.org/LICENSE.txt for license information
+*/
+
+#pragma once
+
+#if __wasi__
+
+#include <errno.h>
+#include <fcntl.h>
+
+// wasi-libc defines the following constants in a way that Clang Importer can't
+// understand, so we need to expose them manually.
+static inline int32_t _getConst_O_ACCMODE(void) { return O_ACCMODE; }
+static inline int32_t _getConst_O_APPEND(void) { return O_APPEND; }
+static inline int32_t _getConst_O_CREAT(void) { return O_CREAT; }
+static inline int32_t _getConst_O_DIRECTORY(void) { return O_DIRECTORY; }
+static inline int32_t _getConst_O_EXCL(void) { return O_EXCL; }
+static inline int32_t _getConst_O_NONBLOCK(void) { return O_NONBLOCK; }
+static inline int32_t _getConst_O_TRUNC(void) { return O_TRUNC; }
+static inline int32_t _getConst_O_WRONLY(void) { return O_WRONLY; }
+
+static inline int32_t _getConst_EWOULDBLOCK(void) { return EWOULDBLOCK; }
+static inline int32_t _getConst_EOPNOTSUPP(void) { return EOPNOTSUPP; }
+
+#endif
diff --git a/Sources/CSystem/include/module.modulemap b/Sources/CSystem/include/module.modulemap
index 776f7766..6e8b89e9 100644
--- a/Sources/CSystem/include/module.modulemap
+++ b/Sources/CSystem/include/module.modulemap
@@ -1,5 +1,6 @@
 module CSystem {
   header "CSystemLinux.h"
+  header "CSystemWASI.h"
   header "CSystemWindows.h"
   export *
 }
diff --git a/Sources/System/Errno.swift b/Sources/System/Errno.swift
index 498ccbcf..093023d0 100644
--- a/Sources/System/Errno.swift
+++ b/Sources/System/Errno.swift
@@ -1,7 +1,7 @@
 /*
  This source file is part of the Swift System open source project
 
- Copyright (c) 2020 Apple Inc. and the Swift System project authors
+ Copyright (c) 2021 - 2024 Apple Inc. and the Swift System project authors
  Licensed under Apache License v2.0 with Runtime Library Exception
 
  See https://swift.org/LICENSE.txt for license information
@@ -226,7 +226,7 @@ public struct Errno: RawRepresentable, Error, Hashable, Codable {
   @available(*, unavailable, renamed: "badAddress")
   public static var EFAULT: Errno { badAddress }
 
-#if !os(Windows)
+#if !os(Windows) && !os(WASI)
   /// Not a block device.
   ///
   /// You attempted a block device operation on a nonblock device or file.
@@ -618,6 +618,7 @@ public struct Errno: RawRepresentable, Error, Hashable, Codable {
   @available(*, unavailable, renamed: "protocolNotSupported")
   public static var EPROTONOSUPPORT: Errno { protocolNotSupported }
 
+#if !os(WASI)
   /// Socket type not supported.
   ///
   /// Support for the socket type hasn't been configured into the system
@@ -630,6 +631,7 @@ public struct Errno: RawRepresentable, Error, Hashable, Codable {
   @_alwaysEmitIntoClient
   @available(*, unavailable, renamed: "socketTypeNotSupported")
   public static var ESOCKTNOSUPPORT: Errno { socketTypeNotSupported }
+#endif
 
   /// Not supported.
   ///
@@ -644,6 +646,7 @@ public struct Errno: RawRepresentable, Error, Hashable, Codable {
   @available(*, unavailable, renamed: "notSupported")
   public static var ENOTSUP: Errno { notSupported }
 
+#if !os(WASI)
   /// Protocol family not supported.
   ///
   /// The protocol family hasn't been configured into the system
@@ -656,6 +659,7 @@ public struct Errno: RawRepresentable, Error, Hashable, Codable {
   @_alwaysEmitIntoClient
   @available(*, unavailable, renamed: "protocolFamilyNotSupported")
   public static var EPFNOSUPPORT: Errno { protocolFamilyNotSupported }
+#endif
 
   /// The address family isn't supported by the protocol family.
   ///
@@ -802,6 +806,7 @@ public struct Errno: RawRepresentable, Error, Hashable, Codable {
   @available(*, unavailable, renamed: "socketNotConnected")
   public static var ENOTCONN: Errno { socketNotConnected }
 
+#if !os(WASI)
   /// Can't send after socket shutdown.
   ///
   /// A request to send data wasn't permitted
@@ -815,6 +820,7 @@ public struct Errno: RawRepresentable, Error, Hashable, Codable {
   @_alwaysEmitIntoClient
   @available(*, unavailable, renamed: "socketShutdown")
   public static var ESHUTDOWN: Errno { socketShutdown }
+#endif
 
   /// Operation timed out.
   ///
@@ -871,6 +877,7 @@ public struct Errno: RawRepresentable, Error, Hashable, Codable {
   @available(*, unavailable, renamed: "fileNameTooLong")
   public static var ENAMETOOLONG: Errno { fileNameTooLong }
 
+#if !os(WASI)
   /// The host is down.
   ///
   /// A socket operation failed because the destination host was down.
@@ -882,6 +889,7 @@ public struct Errno: RawRepresentable, Error, Hashable, Codable {
   @_alwaysEmitIntoClient
   @available(*, unavailable, renamed: "hostIsDown")
   public static var EHOSTDOWN: Errno { hostIsDown }
+#endif
 
   /// No route to host.
   ///
@@ -920,6 +928,7 @@ public struct Errno: RawRepresentable, Error, Hashable, Codable {
   public static var EPROCLIM: Errno { tooManyProcesses }
 #endif
 
+#if !os(WASI)
   /// Too many users.
   ///
   /// The quota system ran out of table entries.
@@ -931,6 +940,7 @@ public struct Errno: RawRepresentable, Error, Hashable, Codable {
   @_alwaysEmitIntoClient
   @available(*, unavailable, renamed: "tooManyUsers")
   public static var EUSERS: Errno { tooManyUsers }
+#endif
 
   /// Disk quota exceeded.
   ///
@@ -1284,6 +1294,7 @@ public struct Errno: RawRepresentable, Error, Hashable, Codable {
   @available(*, unavailable, renamed: "multiHop")
   public static var EMULTIHOP: Errno { multiHop }
 
+#if !os(WASI)
   /// No message available.
   ///
   /// No message was available to be received by the requested operation.
@@ -1295,6 +1306,7 @@ public struct Errno: RawRepresentable, Error, Hashable, Codable {
   @_alwaysEmitIntoClient
   @available(*, unavailable, renamed: "noData")
   public static var ENODATA: Errno { noData }
+#endif
 
   /// Reserved.
   ///
@@ -1308,6 +1320,7 @@ public struct Errno: RawRepresentable, Error, Hashable, Codable {
   @available(*, unavailable, renamed: "noLink")
   public static var ENOLINK: Errno { noLink }
 
+#if !os(WASI)
   /// Reserved.
   ///
   /// This error is reserved for future use.
@@ -1331,6 +1344,7 @@ public struct Errno: RawRepresentable, Error, Hashable, Codable {
   @_alwaysEmitIntoClient
   @available(*, unavailable, renamed: "notStream")
   public static var ENOSTR: Errno { notStream }
+#endif
 #endif
 
   /// Protocol error.
@@ -1347,7 +1361,7 @@ public struct Errno: RawRepresentable, Error, Hashable, Codable {
   @available(*, unavailable, renamed: "protocolError")
   public static var EPROTO: Errno { protocolError }
 
-#if !os(OpenBSD)
+#if !os(OpenBSD) && !os(WASI)
   /// Reserved.
   ///
   /// This error is reserved for future use.
@@ -1379,7 +1393,6 @@ public struct Errno: RawRepresentable, Error, Hashable, Codable {
 // Constants defined in header but not man page
 @available(/*System 0.0.1: macOS 11.0, iOS 14.0, watchOS 7.0, tvOS 14.0*/iOS 8, *)
 extension Errno {
-
   /// Operation would block.
   ///
   /// The corresponding C error is `EWOULDBLOCK`.
@@ -1390,6 +1403,7 @@ extension Errno {
   @available(*, unavailable, renamed: "wouldBlock")
   public static var EWOULDBLOCK: Errno { wouldBlock }
 
+#if !os(WASI)
   /// Too many references: can't splice.
   ///
   /// The corresponding C error is `ETOOMANYREFS`.
@@ -1409,6 +1423,7 @@ extension Errno {
   @_alwaysEmitIntoClient
   @available(*, unavailable, renamed: "tooManyRemoteLevels")
   public static var EREMOTE: Errno { tooManyRemoteLevels }
+#endif
 
 #if SYSTEM_PACKAGE_DARWIN
   /// No such policy registered.
diff --git a/Sources/System/Internals/CInterop.swift b/Sources/System/Internals/CInterop.swift
index 3b4792e8..80d37d05 100644
--- a/Sources/System/Internals/CInterop.swift
+++ b/Sources/System/Internals/CInterop.swift
@@ -1,7 +1,7 @@
 /*
  This source file is part of the Swift System open source project
 
- Copyright (c) 2020 - 2021 Apple Inc. and the Swift System project authors
+ Copyright (c) 2020 - 2024 Apple Inc. and the Swift System project authors
  Licensed under Apache License v2.0 with Runtime Library Exception
 
  See https://swift.org/LICENSE.txt for license information
@@ -18,6 +18,11 @@ import Glibc
 #elseif canImport(Musl)
 @_implementationOnly import CSystem
 import Musl
+#elseif canImport(WASILibc)
+import WASILibc
+#elseif canImport(Bionic)
+@_implementationOnly import CSystem
+import Bionic
 #else
 #error("Unsupported Platform")
 #endif
diff --git a/Sources/System/Internals/Constants.swift b/Sources/System/Internals/Constants.swift
index 8d4e4bb1..904e5b22 100644
--- a/Sources/System/Internals/Constants.swift
+++ b/Sources/System/Internals/Constants.swift
@@ -1,7 +1,7 @@
 /*
  This source file is part of the Swift System open source project
 
- Copyright (c) 2020 - 2021 Apple Inc. and the Swift System project authors
+ Copyright (c) 2020 - 2024 Apple Inc. and the Swift System project authors
  Licensed under Apache License v2.0 with Runtime Library Exception
 
  See https://swift.org/LICENSE.txt for license information
@@ -21,6 +21,11 @@ import Glibc
 #elseif canImport(Musl)
 import CSystem
 import Musl
+#elseif canImport(WASILibc)
+import CSystem
+import WASILibc
+#elseif canImport(Android)
+import Android
 #else
 #error("Unsupported Platform")
 #endif
@@ -73,7 +78,7 @@ internal var _EACCES: CInt { EACCES }
 @_alwaysEmitIntoClient
 internal var _EFAULT: CInt { EFAULT }
 
-#if !os(Windows)
+#if !os(Windows) && !os(WASI)
 @_alwaysEmitIntoClient
 internal var _ENOTBLK: CInt { ENOTBLK }
 #endif
@@ -141,7 +146,13 @@ internal var _ERANGE: CInt { ERANGE }
 internal var _EAGAIN: CInt { EAGAIN }
 
 @_alwaysEmitIntoClient
-internal var _EWOULDBLOCK: CInt { EWOULDBLOCK }
+internal var _EWOULDBLOCK: CInt {
+#if os(WASI)
+  _getConst_EWOULDBLOCK()
+#else
+  EWOULDBLOCK
+#endif
+}
 
 @_alwaysEmitIntoClient
 internal var _EINPROGRESS: CInt { EINPROGRESS }
@@ -167,6 +178,7 @@ internal var _ENOPROTOOPT: CInt { ENOPROTOOPT }
 @_alwaysEmitIntoClient
 internal var _EPROTONOSUPPORT: CInt { EPROTONOSUPPORT }
 
+#if !os(WASI)
 @_alwaysEmitIntoClient
 internal var _ESOCKTNOSUPPORT: CInt {
 #if os(Windows)
@@ -175,6 +187,7 @@ internal var _ESOCKTNOSUPPORT: CInt {
   return ESOCKTNOSUPPORT
 #endif
 }
+#endif
 
 @_alwaysEmitIntoClient
 internal var _ENOTSUP: CInt {
@@ -185,6 +198,7 @@ internal var _ENOTSUP: CInt {
 #endif
 }
 
+#if !os(WASI)
 @_alwaysEmitIntoClient
 internal var _EPFNOSUPPORT: CInt {
 #if os(Windows)
@@ -193,6 +207,7 @@ internal var _EPFNOSUPPORT: CInt {
   return EPFNOSUPPORT
 #endif
 }
+#endif
 
 @_alwaysEmitIntoClient
 internal var _EAFNOSUPPORT: CInt { EAFNOSUPPORT }
@@ -227,6 +242,7 @@ internal var _EISCONN: CInt { EISCONN }
 @_alwaysEmitIntoClient
 internal var _ENOTCONN: CInt { ENOTCONN }
 
+#if !os(WASI)
 @_alwaysEmitIntoClient
 internal var _ESHUTDOWN: CInt {
 #if os(Windows)
@@ -244,6 +260,7 @@ internal var _ETOOMANYREFS: CInt {
   return ETOOMANYREFS
 #endif
 }
+#endif
 
 @_alwaysEmitIntoClient
 internal var _ETIMEDOUT: CInt { ETIMEDOUT }
@@ -257,6 +274,7 @@ internal var _ELOOP: CInt { ELOOP }
 @_alwaysEmitIntoClient
 internal var _ENAMETOOLONG: CInt { ENAMETOOLONG }
 
+#if !os(WASI)
 @_alwaysEmitIntoClient
 internal var _EHOSTDOWN: CInt {
 #if os(Windows)
@@ -265,6 +283,7 @@ internal var _EHOSTDOWN: CInt {
   return EHOSTDOWN
 #endif
 }
+#endif
 
 @_alwaysEmitIntoClient
 internal var _EHOSTUNREACH: CInt { EHOSTUNREACH }
@@ -277,6 +296,7 @@ internal var _ENOTEMPTY: CInt { ENOTEMPTY }
 internal var _EPROCLIM: CInt { EPROCLIM }
 #endif
 
+#if !os(WASI)
 @_alwaysEmitIntoClient
 internal var _EUSERS: CInt {
 #if os(Windows)
@@ -285,6 +305,7 @@ internal var _EUSERS: CInt {
   return EUSERS
 #endif
 }
+#endif
 
 @_alwaysEmitIntoClient
 internal var _EDQUOT: CInt {
@@ -304,6 +325,7 @@ internal var _ESTALE: CInt {
 #endif
 }
 
+#if !os(WASI)
 @_alwaysEmitIntoClient
 internal var _EREMOTE: CInt {
 #if os(Windows)
@@ -312,6 +334,7 @@ internal var _EREMOTE: CInt {
   return EREMOTE
 #endif
 }
+#endif
 
 #if SYSTEM_PACKAGE_DARWIN
 @_alwaysEmitIntoClient
@@ -399,30 +422,41 @@ internal var _EBADMSG: CInt { EBADMSG }
 @_alwaysEmitIntoClient
 internal var _EMULTIHOP: CInt { EMULTIHOP }
 
+#if !os(WASI)
 @_alwaysEmitIntoClient
 internal var _ENODATA: CInt { ENODATA }
+#endif
 
 @_alwaysEmitIntoClient
 internal var _ENOLINK: CInt { ENOLINK }
 
+#if !os(WASI)
 @_alwaysEmitIntoClient
 internal var _ENOSR: CInt { ENOSR }
 
 @_alwaysEmitIntoClient
 internal var _ENOSTR: CInt { ENOSTR }
 #endif 
+#endif
 
 @_alwaysEmitIntoClient
 internal var _EPROTO: CInt { EPROTO }
 
-#if !os(OpenBSD)
+#if !os(OpenBSD) && !os(WASI)
 @_alwaysEmitIntoClient
 internal var _ETIME: CInt { ETIME }
 #endif
 #endif
 
+
 @_alwaysEmitIntoClient
-internal var _EOPNOTSUPP: CInt { EOPNOTSUPP }
+internal var _EOPNOTSUPP: CInt {
+#if os(WASI)
+  _getConst_EOPNOTSUPP()
+#else
+  EOPNOTSUPP
+#endif
+}
 
 #if SYSTEM_PACKAGE_DARWIN
 @_alwaysEmitIntoClient
@@ -462,15 +496,33 @@ internal var _O_ACCMODE: CInt { 0x03|O_SEARCH }
 #else
 // TODO: API?
 @_alwaysEmitIntoClient
-internal var _O_ACCMODE: CInt { O_ACCMODE }
+internal var _O_ACCMODE: CInt {
+#if os(WASI)
+  _getConst_O_ACCMODE()
+#else
+  O_ACCMODE
+#endif
+}
 #endif
 
 @_alwaysEmitIntoClient
-internal var _O_NONBLOCK: CInt { O_NONBLOCK }
+internal var _O_NONBLOCK: CInt {
+#if os(WASI)
+  _getConst_O_NONBLOCK()
+#else
+  O_NONBLOCK
+#endif
+}
 #endif
 
 @_alwaysEmitIntoClient
-internal var _O_APPEND: CInt { O_APPEND }
+internal var _O_APPEND: CInt {
+#if os(WASI)
+  _getConst_O_APPEND()
+#else
+  O_APPEND
+#endif
+}
 
 #if SYSTEM_PACKAGE_DARWIN
 @_alwaysEmitIntoClient
@@ -481,22 +533,42 @@ internal var _O_EXLOCK: CInt { O_EXLOCK }
 #endif
 
 #if !os(Windows)
+#if !os(WASI)
 // TODO: API?
 @_alwaysEmitIntoClient
 internal var _O_ASYNC: CInt { O_ASYNC }
+#endif
 
 @_alwaysEmitIntoClient
 internal var _O_NOFOLLOW: CInt { O_NOFOLLOW }
 #endif
 
 @_alwaysEmitIntoClient
-internal var _O_CREAT: CInt { O_CREAT }
+internal var _O_CREAT: CInt {
+#if os(WASI)
+  _getConst_O_CREAT()
+#else
+  O_CREAT
+#endif
+}
 
 @_alwaysEmitIntoClient
-internal var _O_TRUNC: CInt { O_TRUNC }
+internal var _O_TRUNC: CInt {
+#if os(WASI)
+  _getConst_O_TRUNC()
+#else
+  O_TRUNC
+#endif
+}
 
 @_alwaysEmitIntoClient
-internal var _O_EXCL: CInt { O_EXCL }
+internal var _O_EXCL: CInt {
+#if os(WASI)
+  _getConst_O_EXCL()
+#else
+  O_EXCL
+#endif
+}
 
 #if SYSTEM_PACKAGE_DARWIN
 @_alwaysEmitIntoClient
@@ -509,7 +581,13 @@ internal var _O_EVTONLY: CInt { O_EVTONLY }
 internal var _O_NOCTTY: CInt { O_NOCTTY }
 
 @_alwaysEmitIntoClient
-internal var _O_DIRECTORY: CInt { O_DIRECTORY }
+internal var _O_DIRECTORY: CInt {
+#if os(WASI)
+  _getConst_O_DIRECTORY()
+#else
+  O_DIRECTORY
+#endif
+}
 #endif
 
 #if SYSTEM_PACKAGE_DARWIN
diff --git a/Sources/System/Internals/Exports.swift b/Sources/System/Internals/Exports.swift
index e20454ee..d18102a2 100644
--- a/Sources/System/Internals/Exports.swift
+++ b/Sources/System/Internals/Exports.swift
@@ -1,7 +1,7 @@
 /*
  This source file is part of the Swift System open source project
 
- Copyright (c) 2020 - 2021 Apple Inc. and the Swift System project authors
+ Copyright (c) 2020 - 2024 Apple Inc. and the Swift System project authors
  Licensed under Apache License v2.0 with Runtime Library Exception
 
  See https://swift.org/LICENSE.txt for license information
@@ -23,6 +23,11 @@ import Glibc
 #elseif canImport(Musl)
 @_implementationOnly import CSystem
 import Musl
+#elseif canImport(WASILibc)
+import WASILibc
+#elseif canImport(Android)
+@_implementationOnly import CSystem
+import Android
 #else
 #error("Unsupported Platform")
 #endif
@@ -58,6 +63,16 @@ internal var system_errno: CInt {
   get { Musl.errno }
   set { Musl.errno = newValue }
 }
+#elseif canImport(WASILibc)
+internal var system_errno: CInt {
+  get { WASILibc.errno }
+  set { WASILibc.errno = newValue }
+}
+#elseif canImport(Android)
+internal var system_errno: CInt {
+  get { Android.errno }
+  set { Android.errno = newValue }
+}
 #endif
 
 // MARK: C stdlib decls
@@ -149,6 +164,24 @@ extension String {
 // TLS
 #if os(Windows)
 internal typealias _PlatformTLSKey = DWORD
+#elseif os(WASI) && (swift(<6.1) || !_runtime(_multithreaded))
+// Mock TLS storage for single-threaded WASI
+internal final class _PlatformTLSKey {
+    fileprivate init() {}
+}
+private final class TLSStorage: @unchecked Sendable {
+    var storage = [ObjectIdentifier: UnsafeMutableRawPointer]()
+}
+private let sharedTLSStorage = TLSStorage()
+
+func pthread_setspecific(_ key: _PlatformTLSKey, _ p: UnsafeMutableRawPointer?) -> Int {
+    sharedTLSStorage.storage[ObjectIdentifier(key)] = p
+    return 0
+}
+
+func pthread_getspecific(_ key: _PlatformTLSKey) -> UnsafeMutableRawPointer? {
+    sharedTLSStorage.storage[ObjectIdentifier(key)]
+}
 #else
 internal typealias _PlatformTLSKey = pthread_key_t
 #endif
@@ -160,6 +193,8 @@ internal func makeTLSKey() -> _PlatformTLSKey {
     fatalError("Unable to create key")
   }
   return raw
+  #elseif os(WASI) && (swift(<6.1) || !_runtime(_multithreaded))
+  return _PlatformTLSKey()
   #else
   var raw = pthread_key_t()
   guard 0 == pthread_key_create(&raw, nil) else {
diff --git a/Sources/System/Internals/Syscalls.swift b/Sources/System/Internals/Syscalls.swift
index 3794d6e0..6f885be5 100644
--- a/Sources/System/Internals/Syscalls.swift
+++ b/Sources/System/Internals/Syscalls.swift
@@ -17,6 +17,8 @@ import Musl
 import WASILibc
 #elseif os(Windows)
 import ucrt
+#elseif canImport(Android)
+import Android
 #else
 #error("Unsupported Platform")
 #endif
@@ -189,7 +191,7 @@ internal func system_confstr(
 internal let SYSTEM_AT_REMOVE_DIR = AT_REMOVEDIR
 internal let SYSTEM_DT_DIR = DT_DIR
 internal typealias system_dirent = dirent
-#if os(Linux)
+#if os(Linux) || os(Android)
 internal typealias system_DIRPtr = OpaquePointer
 #else
 internal typealias system_DIRPtr = UnsafeMutablePointer<DIR>