diff --git a/js/globals.ts b/js/globals.ts
index 912af7dc4e..3e40db06cd 100644
--- a/js/globals.ts
+++ b/js/globals.ts
@@ -25,6 +25,8 @@ declare global {
 
     TextEncoder: typeof TextEncoder;
     TextDecoder: typeof TextDecoder;
+    atob: typeof atob;
+    btoa: typeof btoa;
 
     Headers: typeof Headers;
     Blob: typeof Blob;
@@ -43,6 +45,8 @@ declare global {
   // tslint:disable:variable-name
   const TextEncoder: typeof textEncoding.TextEncoder;
   const TextDecoder: typeof textEncoding.TextDecoder;
+  const atob: typeof textEncoding.atob;
+  const btoa: typeof textEncoding.btoa;
   const Headers: typeof DenoHeaders;
   const Blob: typeof DenoBlob;
   // tslint:enable:variable-name
@@ -62,6 +66,8 @@ window.clearInterval = timers.clearTimer;
 window.console = new Console(libdeno.print);
 window.TextEncoder = textEncoding.TextEncoder;
 window.TextDecoder = textEncoding.TextDecoder;
+window.atob = textEncoding.atob;
+window.btoa = textEncoding.btoa;
 
 window.fetch = fetch_.fetch;
 
diff --git a/js/text_encoding.ts b/js/text_encoding.ts
index c8e262f5e9..087bbc952b 100644
--- a/js/text_encoding.ts
+++ b/js/text_encoding.ts
@@ -1,4 +1,45 @@
 // Copyright 2018 the Deno authors. All rights reserved. MIT license.
+import * as base64 from "base64-js";
+import { DenoError, ErrorKind } from "./errors";
+
+export function atob(s: string): string {
+  const rem = s.length % 4;
+  // base64-js requires length exactly times of 4
+  if (rem > 0) {
+    s = s.padEnd(s.length + (4 - rem), "=");
+  }
+  let byteArray;
+  try {
+    byteArray = base64.toByteArray(s);
+  } catch (_) {
+    throw new DenoError(
+      ErrorKind.InvalidInput,
+      "The string to be decoded is not correctly encoded"
+    );
+  }
+  let result = "";
+  for (let i = 0; i < byteArray.length; i++) {
+    result += String.fromCharCode(byteArray[i]);
+  }
+  return result;
+}
+
+export function btoa(s: string): string {
+  const byteArray = [];
+  for (let i = 0; i < s.length; i++) {
+    const charCode = s[i].charCodeAt(0);
+    if (charCode > 0xff) {
+      throw new DenoError(
+        ErrorKind.InvalidInput,
+        "The string to be encoded contains characters " +
+          "outside of the Latin1 range."
+      );
+    }
+    byteArray.push(charCode);
+  }
+  const result = base64.fromByteArray(Uint8Array.from(byteArray));
+  return result;
+}
 
 // @types/text-encoding relies on lib.dom.d.ts for some interfaces. We do not
 // want to include lib.dom.d.ts (due to size) into deno's global type scope.
diff --git a/js/text_encoding_test.ts b/js/text_encoding_test.ts
new file mode 100644
index 0000000000..7a9aec833a
--- /dev/null
+++ b/js/text_encoding_test.ts
@@ -0,0 +1,26 @@
+// Copyright 2018 the Deno authors. All rights reserved. MIT license.
+import { test, assert, assertEqual } from "./test_util.ts";
+
+test(function atobSuccess() {
+  const text = "hello world";
+  const encoded = btoa(text);
+  assertEqual(encoded, "aGVsbG8gd29ybGQ=");
+});
+
+test(function btoaSuccess() {
+  const encoded = "aGVsbG8gd29ybGQ=";
+  const decoded = atob(encoded);
+  assertEqual(decoded, "hello world");
+});
+
+test(function btoaFailed() {
+  const text = "你好";
+  let err;
+  try {
+    btoa(text);
+  } catch (e) {
+    err = e;
+  }
+  assert(!!err);
+  assertEqual(err.name, "InvalidInput");
+});
diff --git a/js/unit_tests.ts b/js/unit_tests.ts
index a535aea551..9b85cf3ec0 100644
--- a/js/unit_tests.ts
+++ b/js/unit_tests.ts
@@ -15,3 +15,4 @@ import "./blob_test.ts";
 import "./timers_test.ts";
 import "./symlink_test.ts";
 import "./platform_test.ts";
+import "./text_encoding_test.ts";