diff --git a/src/cli/modules.c b/src/cli/modules.c
index a3c7f6c1..b00af34b 100644
--- a/src/cli/modules.c
+++ b/src/cli/modules.c
@@ -28,6 +28,7 @@ extern void platformHomePath(WrenVM* vm);
 extern void platformIsPosix(WrenVM* vm);
 extern void platformName(WrenVM* vm);
 extern void processAllArguments(WrenVM* vm);
+extern void processChdir(WrenVM* vm);
 extern void processCwd(WrenVM* vm);
 extern void processPid(WrenVM* vm);
 extern void processPpid(WrenVM* vm);
@@ -176,6 +177,7 @@ static ModuleRegistry modules[] =
     END_CLASS
     CLASS(Process)
       STATIC_METHOD("allArguments", processAllArguments)
+      STATIC_METHOD("chdir_(_)", processChdir)
       STATIC_METHOD("cwd", processCwd)
       STATIC_METHOD("pid", processPid)
       STATIC_METHOD("ppid", processPpid)
diff --git a/src/module/os.c b/src/module/os.c
index c13cd33f..27c40c55 100644
--- a/src/module/os.c
+++ b/src/module/os.c
@@ -98,6 +98,19 @@ void processAllArguments(WrenVM* vm)
   }
 }
 
+// chdir_(dir)
+void processChdir(WrenVM* vm)
+{
+  wrenEnsureSlots(vm, 1);
+  const char* dir = wrenGetSlotString(vm, 1);
+  if (uv_chdir(dir) != 0)
+  {
+    wrenSetSlotString(vm, 0, "Cannot change directory.");
+    wrenAbortFiber(vm, 0);
+    return;
+  }
+}
+
 void processCwd(WrenVM* vm)
 {
   wrenEnsureSlots(vm, 1);
diff --git a/src/module/os.wren b/src/module/os.wren
index 4d9ec25a..90bb62b3 100644
--- a/src/module/os.wren
+++ b/src/module/os.wren
@@ -10,8 +10,19 @@ class Process {
   // TODO: This will need to be smarter when wren supports CLI options.
   static arguments { allArguments.count >= 2 ? allArguments[2..-1] : [] }
 
+  static chdir(dir) {
+    ensureString_(dir, "directory")
+    chdir_(dir)
+  }
+
+  // TODO: Copied from `io`. Figure out good way to share this.
+  static ensureString_(s, name) {
+    if (!(s is String)) Fiber.abort("%(name) must be a string.")
+  }
+
   foreign static allArguments
   foreign static cwd
+  foreign static chdir_(dir)
   foreign static pid
   foreign static ppid
   foreign static version
diff --git a/src/module/os.wren.inc b/src/module/os.wren.inc
index 8c7c8522..32ac4295 100644
--- a/src/module/os.wren.inc
+++ b/src/module/os.wren.inc
@@ -14,8 +14,19 @@ static const char* osModuleSource =
 "  // TODO: This will need to be smarter when wren supports CLI options.\n"
 "  static arguments { allArguments.count >= 2 ? allArguments[2..-1] : [] }\n"
 "\n"
+"  static chdir(dir) {\n"
+"    ensureString_(dir, \"directory\")\n"
+"    chdir_(dir)\n"
+"  }\n"
+"\n"
+"  // TODO: Copied from `io`. Figure out good way to share this.\n"
+"  static ensureString_(s, name) {\n"
+"    if (!(s is String)) Fiber.abort(\"%(name) must be a string.\")\n"
+"  }\n"
+"\n"
 "  foreign static allArguments\n"
 "  foreign static cwd\n"
+"  foreign static chdir_(dir)\n"
 "  foreign static pid\n"
 "  foreign static ppid\n"
 "  foreign static version\n"