diff --git a/bootstrap.php b/bootstrap.php
index 7891748..a6a61f2 100644
--- a/bootstrap.php
+++ b/bootstrap.php
@@ -19,6 +19,7 @@ function ml_get_lisp(): array
     // Register libraries
     (new MadLisp\Lib\Collections())->register($env);
     (new MadLisp\Lib\Compare())->register($env);
+    (new MadLisp\Lib\IO())->register($env);
     (new MadLisp\Lib\Math())->register($env);
     (new MadLisp\Lib\Strings())->register($env);
     (new MadLisp\Lib\Time())->register($env);
diff --git a/src/Lib/IO.php b/src/Lib/IO.php
new file mode 100644
index 0000000..f197d9f
--- /dev/null
+++ b/src/Lib/IO.php
@@ -0,0 +1,34 @@
+<?php
+namespace MadLisp\Lib;
+
+use MadLisp\CoreFunc;
+use MadLisp\Env;
+
+class IO implements ILib
+{
+    public function register(Env $env): void
+    {
+        $env->set('file?', new CoreFunc('file?', 'Check if file exists.', 1, 1,
+            fn (string $filename) => file_exists($filename)
+        ));
+
+        $env->set('fread', new CoreFunc('fread', 'Read contents of a file.', 1, 1,
+            function (string $filename) {
+                return @file_get_contents($filename);
+            }
+        ));
+
+        $env->set('fwrite', new CoreFunc('fwrite', 'Write string (second argument) to file (first argument). Give true as optional third argument to append instead of overwrite.', 2, 3,
+            function (string $filename, $data, $append = false) {
+                $flags = 0;
+                if ($append) {
+                    $flags = \FILE_APPEND;
+                }
+
+                $result = @file_put_contents($filename, $data, $flags);
+
+                return $result !== false;
+            }
+        ));
+    }
+}