diff --git a/CMakeLists.txt b/CMakeLists.txt
index 1871be8c..28ab24ef 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -55,6 +55,7 @@ src/core/gc.c
 src/core/io.c
 src/core/math.c
 src/core/native.c
+src/core/os.c
 src/core/string.c
 src/core/struct.c
 src/core/symcache.c
diff --git a/src/compiler/stl.c b/src/compiler/stl.c
index eb7f23c1..60e84dc3 100644
--- a/src/compiler/stl.c
+++ b/src/compiler/stl.c
@@ -109,6 +109,7 @@ DstTable *dst_stl_env() {
         dst_lib_buffer(args);
         dst_lib_table(args);
         dst_lib_fiber(args);
+        dst_lib_os(args);
         dst_lib_parse(args);
         dst_lib_compile(args);
         dst_lib_asm(args);
diff --git a/src/core/os.c b/src/core/os.c
new file mode 100644
index 00000000..be97e405
--- /dev/null
+++ b/src/core/os.c
@@ -0,0 +1,101 @@
+/*
+* Copyright (c) 2017 Calvin Rose
+*
+* 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.
+*/
+
+#include <dst/dst.h>
+
+#include <stdlib.h>
+
+static int os_execute(DstArgs args) {
+    int nofirstarg = (args.n < 1 || !dst_checktype(args.v[0], DST_STRING));
+    const char *cmd = nofirstarg 
+        ? NULL
+        : (const char *) dst_unwrap_string(args.v[0]);
+    int stat = system(cmd);
+    return dst_return(args, cmd
+            ? dst_wrap_integer(stat)
+            : dst_wrap_boolean(stat));
+}
+
+static int os_getenv(DstArgs args) {
+    if (args.n != 1 || !dst_checktype(args.v[0], DST_STRING))
+        return dst_throw(args, "expected string");
+    const char *cstr = (const char *) dst_unwrap_string(args.v[0]);
+    const char *res = getenv(cstr);
+    return dst_return(args, cstr
+            ? dst_cstringv(res)
+            : dst_wrap_nil());
+}
+
+static int os_setenv(DstArgs args) {
+    int t2;
+    if (args.n < 2) return dst_throw(args, "expected 2 arguments");
+    t2 = dst_type(args.v[1]);
+    if (!dst_checktype(args.v[0], DST_STRING)
+        || (t2 != DST_STRING && t2 != DST_NIL))
+        return dst_throw(args, "expected string");
+    const char *k = (const char *) dst_unwrap_string(args.v[0]);
+#ifdef DST_WINDOWS
+    if (t2 == DST_NIL) {
+        // Investigate best way to delete env vars on windows. Use winapi?
+        _putenv_s(k, "");
+    } else {
+        const char *v = (const char *) dst_unwrap_string(args.v[1]);
+        _putenv_s(k, v);
+    }
+#else
+    if (t2 == DST_NIL) {
+        unsetenv(k);
+    } else {
+        const char *v = (const char *) dst_unwrap_string(args.v[1]);
+        setenv(k, v, 1);
+    }
+#endif
+    return 0;
+}
+
+static int os_exit(DstArgs args) {
+  if (args.n == 0) {
+      exit(EXIT_SUCCESS);
+  } else if (dst_checktype(args.v[0], DST_TRUE)
+          || dst_checktype(args.v[0], DST_FALSE)) {
+      exit(dst_unwrap_boolean(args.v[0]) ? EXIT_SUCCESS : EXIT_FAILURE);
+      return 0;
+  } else {
+      exit(dst_hash(args.v[0]));
+  }
+  return 0;
+}
+
+static const DstReg cfuns[] = {
+    {"os-execute", os_execute},
+    {"os-exit", os_exit},
+    {"os-getenv", os_getenv},
+    {"os-setenv", os_setenv},
+    {NULL, NULL}
+};
+
+/* Module entry point */
+int dst_lib_os(DstArgs args) {
+    DstTable *env = dst_env_arg(args);
+    dst_env_cfuns(env, cfuns);
+    return 0;
+}
diff --git a/src/include/dst/dst.h b/src/include/dst/dst.h
index 1cbe86f6..ebb390b6 100644
--- a/src/include/dst/dst.h
+++ b/src/include/dst/dst.h
@@ -27,12 +27,13 @@
 extern "C" {
 #endif
 
+#include "dstconfig.h"
+
 #include <stdint.h>
 #include <string.h>
 #include <stdlib.h>
 #include <stdarg.h>
 
-#include "dstconfig.h"
 #include "dsttypes.h"
 #include "dststate.h"
 
diff --git a/src/include/dst/dstconfig.h b/src/include/dst/dstconfig.h
index 9f99df58..cc9991e4 100644
--- a/src/include/dst/dstconfig.h
+++ b/src/include/dst/dstconfig.h
@@ -27,7 +27,6 @@
 extern "C" {
 #endif
 
-#include <stdint.h>
 
 #define DST_VERSION "0.0.0 alpha"
 
@@ -50,6 +49,8 @@ extern "C" {
     || defined(sun) || defined(__sun) /* Solaris */ \
     || defined(unix) || defined(__unix) || defined(__unix__)
 #define DST_UNIX 1
+/* Enable certain posix features */
+#define _POSIX_C_SOURCE 200112L
 #elif defined(__EMSCRIPTEN__)
 #define DST_WEB 1
 #elif defined(WIN32) || defined(_WIN32)
@@ -89,6 +90,9 @@ extern "C" {
 #define DST_LITTLE_ENDIAN 1
 #endif
 
+/* Include default headers */
+#include <stdint.h>
+
 /* Handle runtime errors */
 #ifndef dst_exit
 #include <stdlib.h>
diff --git a/src/include/dst/dstcorelib.h b/src/include/dst/dstcorelib.h
index 180f9087..da862b32 100644
--- a/src/include/dst/dstcorelib.h
+++ b/src/include/dst/dstcorelib.h
@@ -111,6 +111,7 @@ int dst_lib_tuple(DstArgs args);
 int dst_lib_buffer(DstArgs args);
 int dst_lib_table(DstArgs args);
 int dst_lib_fiber(DstArgs args);
+int dst_lib_os(DstArgs args);
 
 /* Useful for compiler */
 Dst dst_op_add(Dst lhs, Dst rhs);