diff --git a/src/libcore/os.rs b/src/libcore/os.rs
index 329172bb69ad9..be50c71697fe1 100644
--- a/src/libcore/os.rs
+++ b/src/libcore/os.rs
@@ -30,7 +30,7 @@ export close, fclose, fsync_fd, waitpid;
 export env, getenv, setenv, fdopen, pipe;
 export getcwd, dll_filename, self_exe_path;
 export exe_suffix, dll_suffix, sysname, arch, family;
-export homedir, list_dir, list_dir_path, path_is_dir, path_exists,
+export homedir, tmpdir, list_dir, list_dir_path, path_is_dir, path_exists,
        make_absolute, make_dir, remove_dir, change_dir, remove_file,
        copy_file;
 export last_os_error;
@@ -464,6 +464,46 @@ fn homedir() -> option<Path> {
     }
 }
 
+/**
+ * Returns the path to a temporary directory.
+ *
+ * On Unix, returns the value of the 'TMPDIR' environment variable if it is
+ * set and non-empty and '/tmp' otherwise.
+ *
+ * On Windows, returns the value of, in order, the 'TMP', 'TEMP',
+ * 'USERPROFILE' environment variable  if any are set and not the empty
+ * string. Otherwise, tmpdir returns the path to the Windows directory.
+ */
+fn tmpdir() -> Path {
+    return lookup();
+
+    fn getenv_nonempty(v: Path) -> option<Path> {
+        match getenv(v) {
+            some(x) =>
+                if str::is_empty(x) {
+                    none
+                } else {
+                    some(x)
+                },
+            _ => none
+        }
+    }
+
+    #[cfg(unix)]
+    fn lookup() -> Path {
+        option::get_default(getenv_nonempty(~"TMPDIR"), ~"/tmp")
+    }
+
+    #[cfg(windows)]
+    fn lookup() -> Path {
+        option::get_default(
+                    option::or(getenv_nonempty(~"TMP"),
+                    option::or(getenv_nonempty(~"TEMP"),
+                    option::or(getenv_nonempty(~"USERPROFILE"),
+                               getenv_nonempty(~"WINDIR")))),
+                    ~"C:\\Windows")
+    }
+}
 /// Recursively walk a directory structure
 fn walk_dir(p: Path, f: fn(Path) -> bool) {
 
@@ -931,6 +971,11 @@ mod tests {
                                |s| setenv(~"USERPROFILE", s));
     }
 
+    #[test]
+    fn tmpdir() {
+        assert !str::is_empty(os::tmpdir());
+    }
+
     // Issue #712
     #[test]
     fn test_list_dir_no_invalid_memory_access() { os::list_dir(~"."); }