diff --git a/.github/workflows/ports_unix.yml b/.github/workflows/ports_unix.yml
index 662121654e4f7..7895db4773d45 100644
--- a/.github/workflows/ports_unix.yml
+++ b/.github/workflows/ports_unix.yml
@@ -282,3 +282,17 @@ jobs:
     - name: Print failures
       if: failure()
       run: tests/run-tests.py --print-failures
+
+  wasi:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - name: Install packages
+      run: source tools/ci.sh && ci_unix_wasi_setup
+    - name: Build
+      run: source tools/ci.sh && ci_unix_wasi_build
+    - name: Run main test suite
+      run: source tools/ci.sh && ci_unix_wasi_run_tests
+    - name: Print failures
+      if: failure()
+      run: tests/run-tests.py --print-failures
diff --git a/ports/unix/Makefile b/ports/unix/Makefile
index 3c54d156c31ba..f5edd8d990ff0 100644
--- a/ports/unix/Makefile
+++ b/ports/unix/Makefile
@@ -31,7 +31,11 @@ QSTR_DEFS += qstrdefsport.h
 QSTR_GLOBAL_DEPENDENCIES += $(VARIANT_DIR)/mpconfigvariant.h
 
 # OS name, for simple autoconfig
+ifeq ($(VARIANT),wasi)
+UNAME_S := wasi
+else
 UNAME_S := $(shell uname -s)
+endif
 
 # include py core make definitions
 include $(TOP)/py/py.mk
@@ -107,7 +111,7 @@ CC = clang
 endif
 # Use clang syntax for map file
 LDFLAGS_ARCH = -Wl,-map,$@.map -Wl,-dead_strip
-else
+else ifeq ($(UNAME_S),Linux)
 # Use gcc syntax for map file
 LDFLAGS_ARCH = -Wl,-Map=$@.map,--cref -Wl,--gc-sections
 endif
@@ -303,6 +307,21 @@ $(BUILD)/lib/libffi/include/ffi.h: $(TOP)/lib/libffi/configure
 PREFIX = /usr/local
 BINDIR = $(DESTDIR)$(PREFIX)/bin
 
+ifeq ($(VARIANT),wasi)
+# LLVM still uses the older version of EH proposal. ("phase 3")
+# Convert to the latest version of EH proposal with exnref.
+$(BUILD)/$(PROG).spilled.exnref: $(BUILD)/$(PROG).spilled
+	$(WASM_OPT) --translate-to-exnref --enable-exception-handling \
+	-o $(BUILD)/$(PROG).spilled.exnref $(BUILD)/$(PROG).spilled
+
+# Unlike emscripten, WASI doesn't provide a way to scan GC roots
+# like WASM locals. Hopefully --spill-pointers can workaround it.
+$(BUILD)/$(PROG).spilled: $(BUILD)/$(PROG)
+	$(WASM_OPT) --spill-pointers -o $(BUILD)/$(PROG).spilled $(BUILD)/$(PROG)
+
+all: $(BUILD)/$(PROG).spilled.exnref
+endif
+
 install: $(BUILD)/$(PROG)
 	install -d $(BINDIR)
 	install $(BUILD)/$(PROG) $(BINDIR)/$(PROG)
diff --git a/ports/unix/mpconfigport.h b/ports/unix/mpconfigport.h
index 21ce75a351e98..44b3f74c8c5ee 100644
--- a/ports/unix/mpconfigport.h
+++ b/ports/unix/mpconfigport.h
@@ -155,7 +155,9 @@ typedef long mp_off_t;
 #define MICROPY_PY_SYS_PATH_ARGV_DEFAULTS (0)
 
 // Enable sys.executable.
+#ifndef MICROPY_PY_SYS_EXECUTABLE
 #define MICROPY_PY_SYS_EXECUTABLE (1)
+#endif
 
 #define MICROPY_PY_SOCKET_LISTEN_BACKLOG_DEFAULT (SOMAXCONN < 128 ? SOMAXCONN : 128)
 
diff --git a/ports/unix/unix_mphal.c b/ports/unix/unix_mphal.c
index 5f5abc2e056f6..7af646888f505 100644
--- a/ports/unix/unix_mphal.c
+++ b/ports/unix/unix_mphal.c
@@ -43,7 +43,13 @@
 #endif
 #endif
 
-#ifndef _WIN32
+#if defined(_WIN32) || defined(__wasi__)
+#define HAS_SIGNAL 0
+#else
+#define HAS_SIGNAL 1
+#endif
+
+#if HAS_SIGNAL
 #include <signal.h>
 
 static void sighandler(int signum) {
@@ -75,7 +81,7 @@ static void sighandler(int signum) {
 void mp_hal_set_interrupt_char(char c) {
     // configure terminal settings to (not) let ctrl-C through
     if (c == CHAR_CTRL_C) {
-        #ifndef _WIN32
+        #if HAS_SIGNAL
         // enable signal handler
         struct sigaction sa;
         sa.sa_flags = 0;
@@ -84,7 +90,7 @@ void mp_hal_set_interrupt_char(char c) {
         sigaction(SIGINT, &sa, NULL);
         #endif
     } else {
-        #ifndef _WIN32
+        #if HAS_SIGNAL
         // disable signal handler
         struct sigaction sa;
         sa.sa_flags = 0;
diff --git a/ports/unix/variants/mpconfigvariant_common.h b/ports/unix/variants/mpconfigvariant_common.h
index 9eeed8797366c..24f9f4d4a59b2 100644
--- a/ports/unix/variants/mpconfigvariant_common.h
+++ b/ports/unix/variants/mpconfigvariant_common.h
@@ -95,7 +95,9 @@
 #define MICROPY_PY_OS_INCLUDEFILE      "ports/unix/modos.c"
 #define MICROPY_PY_OS_ERRNO            (1)
 #define MICROPY_PY_OS_GETENV_PUTENV_UNSETENV (1)
+#ifndef MICROPY_PY_OS_SYSTEM
 #define MICROPY_PY_OS_SYSTEM           (1)
+#endif
 #define MICROPY_PY_OS_URANDOM          (1)
 
 // Enable the unix-specific "time" module.
@@ -111,11 +113,15 @@
 #endif
 
 // The "select" module is enabled by default, but disable select.select().
+#ifndef MICROPY_PY_SELECT_POSIX_OPTIMISATIONS
 #define MICROPY_PY_SELECT_POSIX_OPTIMISATIONS (1)
+#endif
 #define MICROPY_PY_SELECT_SELECT       (0)
 
 // Enable the "websocket" module.
+#ifndef MICROPY_PY_WEBSOCKET
 #define MICROPY_PY_WEBSOCKET           (1)
+#endif
 
 // Enable the "machine" module, mostly for machine.mem*.
 #define MICROPY_PY_MACHINE             (1)
diff --git a/ports/unix/variants/wasi/mpconfigvariant.h b/ports/unix/variants/wasi/mpconfigvariant.h
new file mode 100644
index 0000000000000..390926d5a27e9
--- /dev/null
+++ b/ports/unix/variants/wasi/mpconfigvariant.h
@@ -0,0 +1,42 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2019 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+// Set base feature level.
+#define MICROPY_CONFIG_ROM_LEVEL (MICROPY_CONFIG_ROM_LEVEL_EXTRA_FEATURES)
+
+// WASI has different values for POLL constants.
+#define MICROPY_PY_SELECT_POSIX_OPTIMISATIONS (0)
+
+// WASI doesn't have executable or process.
+#define MICROPY_PY_OS_SYSTEM (0)
+#define MICROPY_PY_SYS_EXECUTABLE (0)
+
+// Network support is limited in WASI.
+// WebSocket isn't too useful without network.
+#define MICROPY_PY_WEBSOCKET (0)
+
+// Enable extra Unix features.
+#include "../mpconfigvariant_common.h"
diff --git a/ports/unix/variants/wasi/mpconfigvariant.mk b/ports/unix/variants/wasi/mpconfigvariant.mk
new file mode 100644
index 0000000000000..b4634ddb41707
--- /dev/null
+++ b/ports/unix/variants/wasi/mpconfigvariant.mk
@@ -0,0 +1,47 @@
+# prerequisites
+#
+# WASI_SDK: wasi-sdk 25.0 or later
+# WASM_OPT: binaryen wasm-opt version_117 or later
+
+# Note:
+# we specify the target "--target=wasm32-wasi" explicitly below for the case
+# where $CLANG is built with a configuration different from wasi-sdk.
+# ditto for "-B $(WASI_SDK)/bin/".
+
+WASI_SDK = /opt/wasi-sdk-25.0
+WASI_SYSROOT = $(WASI_SDK)/share/wasi-sysroot
+WASM_OPT = wasm-opt
+RESOURCE_DIR = $(shell $(WASI_SDK)/bin/clang --print-resource-dir)
+CLANG = $(WASI_SDK)/bin/clang
+
+CC = $(CLANG) --sysroot $(WASI_SYSROOT) -resource-dir $(RESOURCE_DIR)
+STRIP = $(WASI_SDK)/bin/strip
+SIZE = $(WASI_SDK)/bin/size
+
+CFLAGS += --target=wasm32-wasi -D_WASI_EMULATED_PROCESS_CLOCKS -D_WASI_EMULATED_SIGNAL -D_WASI_EMULATED_MMAN -mllvm -wasm-enable-sjlj
+LDFLAGS += --target=wasm32-wasi -lwasi-emulated-process-clocks -lwasi-emulated-signal -lwasi-emulated-mman -lsetjmp -B $(WASI_SDK)/bin/
+
+# WASI doesn't have FFI
+MICROPY_PY_FFI = 0
+
+# When threading is enabled, micropython GC uses signals, which is
+# not available on WASI.
+MICROPY_PY_THREAD = 0
+
+# Disable for now because network support is limited in WASI.
+MICROPY_PY_SOCKET = 0
+MICROPY_PY_SSL = 0
+
+# ../../lib/berkeley-db-1.xx/PORT/include/db.h:40:10:
+# fatal error: 'sys/cdefs.h' file not found
+MICROPY_PY_BTREE = 0
+
+# WASI doesn't have termios
+MICROPY_PY_TERMIOS = 0
+MICROPY_USE_READLINE = 0
+
+# The following things might just work as they are.
+# Disabled for now because I'm not interested in them.
+MICROPY_VFS_FAT = 0
+MICROPY_VFS_LFS1 = 0
+MICROPY_VFS_LFS2 = 0
diff --git a/tests/run-tests.py b/tests/run-tests.py
index 628fde9d30a4c..68edf43b5f27d 100755
--- a/tests/run-tests.py
+++ b/tests/run-tests.py
@@ -447,8 +447,9 @@ def send_get(what):
             cmdlist = [os.path.abspath(MICROPYTHON), "-X", "emit=" + args.emit]
             if args.heapsize is not None:
                 cmdlist.extend(["-X", "heapsize=" + args.heapsize])
-            if sys.platform == "darwin":
-                cmdlist.extend(["-X", "realtime"])
+            if os.getenv("MICROPY_MICROPYTHON_WASM") is None:
+                if sys.platform == "darwin":
+                    cmdlist.extend(["-X", "realtime"])
 
             cwd = os.path.dirname(test_file)
 
diff --git a/tools/ci.sh b/tools/ci.sh
index b0e59509add83..2c19bf4efe4cf 100755
--- a/tools/ci.sh
+++ b/tools/ci.sh
@@ -852,6 +852,36 @@ function ci_unix_qemu_riscv64_run_tests {
     (cd tests && MICROPY_MICROPYTHON=../ports/unix/build-coverage/micropython ./run-tests.py)
 }
 
+function ci_unix_wasi_setup {
+    wget https://github.com/WebAssembly/binaryen/releases/download/version_123/binaryen-version_123-x86_64-linux.tar.gz
+    zcat binaryen-version_123-x86_64-linux.tar.gz | tar x
+    wget https://github.com/WebAssembly/wasi-sdk/releases/download/wasi-sdk-25/wasi-sdk-25.0-x86_64-linux.tar.gz
+    zcat wasi-sdk-25.0-x86_64-linux.tar.gz | tar x
+    wget https://github.com/yamt/toywasm/releases/download/v68.0.0/toywasm-v68.0.0-full-ubuntu-22.04-amd64.tgz
+    mkdir toywasm
+    zcat toywasm-v68.0.0-full-ubuntu-22.04-amd64.tgz | tar -C toywasm -x
+}
+
+function ci_unix_wasi_build {
+    make ${MAKEOPTS} -C ports/unix VARIANT=wasi \
+        WASI_SDK=$(pwd -P)/wasi-sdk-25.0-x86_64-linux \
+        WASM_OPT=$(pwd -P)/binaryen-version_123/bin/wasm-opt \
+        submodules
+    make ${MAKEOPTS} -C ports/unix VARIANT=wasi \
+        WASI_SDK=$(pwd -P)/wasi-sdk-25.0-x86_64-linux \
+        WASM_OPT=$(pwd -P)/binaryen-version_123/bin/wasm-opt
+}
+
+function ci_unix_wasi_run_tests {
+    # Note: for simplicity, use absolute path where possible
+    # because wasi doesn't have the concept of "current directory" natively.
+    (cd tests && \
+    MICROPY_MICROPYTHON=$(pwd -P)/../tools/run-with-toywasm.sh \
+    TOYWASM=$(pwd -P)/../toywasm/bin/toywasm \
+    MICROPY_MICROPYTHON_WASM=$(pwd -P)/../ports/unix/build-wasi/micropython.spilled.exnref \
+    ./run-tests.py -d $(pwd -P)/basics)
+}
+
 ########################################################################################
 # ports/windows
 
diff --git a/tools/run-with-toywasm.sh b/tools/run-with-toywasm.sh
new file mode 100755
index 0000000000000..e1da14e1c4fac
--- /dev/null
+++ b/tools/run-with-toywasm.sh
@@ -0,0 +1,10 @@
+#! /bin/sh
+
+if [ ! -e "${MICROPY_MICROPYTHON_WASM}" ]; then
+    echo "MICROPY_MICROPYTHON_WASM is not set properly" >&2
+    exit 1
+fi
+
+exec ${TOYWASM:-toywasm} --wasi --wasi-dir=/ \
+${MICROPY_MICROPYTHON_WASM} \
+-- "$@"