diff --git a/README.md b/README.md
index 1d271f2..471ad83 100644
--- a/README.md
+++ b/README.md
@@ -197,6 +197,8 @@ Name    | Example | Example result | Description
 
 Name    | Example | Example result | Description
 ------- | ------- | -------------- | -----------
+wd      | `(wd)` | `"/home/pekka/code/madlisp/"` | Get the current working directory.
+chdir   | `(chdir "/tmp")` | `true` | Change the current working directory.
 file?   | `(file? "test.txt")` | `true` | Return true if the file exists.
 fread   | `(fread "test.txt")` | `"content"` | Read the contents of a file.
 fwrite  | `(fwrite "test.txt" "content")` | `true` | Write string to file. Give optional third parameter as `true` to append.
@@ -284,8 +286,10 @@ The following constants are defined by default:
 
 Name    | PHP constant
 ------- | ------------
-pi      | M_PI
+dirsep  | DIRECTORY_SEPARATOR
+homedir | $_SERVER['HOME']
 ln      | PHP_EOL
+pi      | M_PI
 
 ## Extending
 
diff --git a/src/Lib/IO.php b/src/Lib/IO.php
index f197d9f..e15859e 100644
--- a/src/Lib/IO.php
+++ b/src/Lib/IO.php
@@ -8,6 +8,17 @@ class IO implements ILib
 {
     public function register(Env $env): void
     {
+        $env->set('dirsep', \DIRECTORY_SEPARATOR);
+        $env->set('homedir', $_SERVER['HOME'] . \DIRECTORY_SEPARATOR);
+
+        $env->set('wd', new CoreFunc('wd', 'Get the current working directory.', 0, 0,
+            fn () => getcwd() . \DIRECTORY_SEPARATOR
+        ));
+
+        $env->set('chdir', new CoreFunc('chdir', 'Change working directory.', 1, 1,
+            fn (string $dir) => chdir($dir)
+        ));
+
         $env->set('file?', new CoreFunc('file?', 'Check if file exists.', 1, 1,
             fn (string $filename) => file_exists($filename)
         ));