diff --git a/doc/api/buffer.md b/doc/api/buffer.md
index ab357fe12486f1d..3826ee89bdcf3cb 100644
--- a/doc/api/buffer.md
+++ b/doc/api/buffer.md
@@ -3279,6 +3279,28 @@ While, the `Buffer` object is available as a global, there are additional
 `Buffer`-related APIs that are available only via the `buffer` module
 accessed using `require('buffer')`.
 
+### `buffer.atob(data)`
+<!-- YAML
+added: REPLACEME
+-->
+
+* `data` {any} The Base64-encoded input string.
+
+Decodes a string of Base64-encoded data into ASCII (Latin1).
+
+The `data` may be any JavaScript-value that can be coerced into a string.
+
+### `buffer.btoa(data)`
+<!-- YAML
+added: REPLACEME
+-->
+
+* `data` {any} An ASCII (Latin1) string.
+
+Encodes a string of ASCII characters into a Base64-encoded string.
+
+The `data` may be any JavaScript-value that can be coerced into a string.
+
 ### `buffer.INSPECT_MAX_BYTES`
 <!-- YAML
 added: v0.5.4
diff --git a/lib/buffer.js b/lib/buffer.js
index 893f5b1915c4d30..951805870c58706 100644
--- a/lib/buffer.js
+++ b/lib/buffer.js
@@ -1211,6 +1211,40 @@ if (internalBinding('config').hasIntl) {
   };
 }
 
+let DOMException;
+
+const lazyInvalidCharError = hideStackFrames((message, name) => {
+  if (DOMException === undefined)
+    DOMException = internalBinding('messaging').DOMException;
+  throw new DOMException('Invalid character', 'InvalidCharacterError');
+});
+
+function btoa(input) {
+  // TODO(@jasnell): The implementation here has not been performance
+  // optimized in any way.
+  input = `${input}`;
+  for (let n = 0; n < input.length; n++) {
+    if (input[n].charCodeAt(0) > 0xff)
+      lazyInvalidCharError();
+  }
+  const buf = Buffer.from(input, 'latin1');
+  return buf.toString('base64');
+}
+
+const kBase64Digits =
+  'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=';
+
+function atob(input) {
+  // TODO(@jasnell): The implementation here has not been performance
+  // optimized in any way.
+  input = `${input}`;
+  for (let n = 0; n < input.length; n++) {
+    if (!kBase64Digits.includes(input[n]))
+      lazyInvalidCharError();
+  }
+  return Buffer.from(input, 'base64').toString('latin1');
+}
+
 module.exports = {
   Blob,
   Buffer,
@@ -1218,7 +1252,9 @@ module.exports = {
   transcode,
   // Legacy
   kMaxLength,
-  kStringMaxLength
+  kStringMaxLength,
+  btoa,
+  atob,
 };
 
 ObjectDefineProperties(module.exports, {
diff --git a/test/fixtures/wpt/README.md b/test/fixtures/wpt/README.md
index a3cbbe667434e2e..f873123a2e3ab5e 100644
--- a/test/fixtures/wpt/README.md
+++ b/test/fixtures/wpt/README.md
@@ -10,17 +10,18 @@ See [test/wpt](../../wpt/README.md) for information on how these tests are run.
 
 Last update:
 
+- common: https://github.com/web-platform-tests/wpt/tree/841a51412f/common
 - console: https://github.com/web-platform-tests/wpt/tree/3b1f72e99a/console
+- dom/abort: https://github.com/web-platform-tests/wpt/tree/7caa3de747/dom/abort
 - encoding: https://github.com/web-platform-tests/wpt/tree/3c9820d1cc/encoding
-- url: https://github.com/web-platform-tests/wpt/tree/1783c9bccf/url
-- resources: https://github.com/web-platform-tests/wpt/tree/351a99782b/resources
-- interfaces: https://github.com/web-platform-tests/wpt/tree/b4be9a3fdf/interfaces
+- FileAPI: https://github.com/web-platform-tests/wpt/tree/3b279420d4/FileAPI
+- hr-time: https://github.com/web-platform-tests/wpt/tree/a5d1774ecf/hr-time
+- html/webappapis/atob: https://github.com/web-platform-tests/wpt/tree/f267e1dca6/html/webappapis/atob
 - html/webappapis/microtask-queuing: https://github.com/web-platform-tests/wpt/tree/2c5c3c4c27/html/webappapis/microtask-queuing
 - html/webappapis/timers: https://github.com/web-platform-tests/wpt/tree/264f12bc7b/html/webappapis/timers
-- hr-time: https://github.com/web-platform-tests/wpt/tree/a5d1774ecf/hr-time
-- common: https://github.com/web-platform-tests/wpt/tree/841a51412f/common
-- dom/abort: https://github.com/web-platform-tests/wpt/tree/7caa3de747/dom/abort
-- FileAPI: https://github.com/web-platform-tests/wpt/tree/3b279420d4/FileAPI
+- interfaces: https://github.com/web-platform-tests/wpt/tree/b4be9a3fdf/interfaces
+- resources: https://github.com/web-platform-tests/wpt/tree/351a99782b/resources
+- url: https://github.com/web-platform-tests/wpt/tree/1783c9bccf/url
 
 [Web Platform Tests]: https://github.com/web-platform-tests/wpt
 [`git node wpt`]: https://github.com/nodejs/node-core-utils/blob/master/docs/git-node.md#git-node-wpt
diff --git a/test/fixtures/wpt/html/webappapis/atob/base64.any.js b/test/fixtures/wpt/html/webappapis/atob/base64.any.js
new file mode 100644
index 000000000000000..7f433f4d8a9ee2e
--- /dev/null
+++ b/test/fixtures/wpt/html/webappapis/atob/base64.any.js
@@ -0,0 +1,163 @@
+/**
+ * btoa() as defined by the HTML5 spec, which mostly just references RFC4648.
+ */
+function mybtoa(s) {
+    // String conversion as required by WebIDL.
+    s = String(s);
+
+    // "The btoa() method must throw an INVALID_CHARACTER_ERR exception if the
+    // method's first argument contains any character whose code point is
+    // greater than U+00FF."
+    for (var i = 0; i < s.length; i++) {
+        if (s.charCodeAt(i) > 255) {
+            return "INVALID_CHARACTER_ERR";
+        }
+    }
+
+    var out = "";
+    for (var i = 0; i < s.length; i += 3) {
+        var groupsOfSix = [undefined, undefined, undefined, undefined];
+        groupsOfSix[0] = s.charCodeAt(i) >> 2;
+        groupsOfSix[1] = (s.charCodeAt(i) & 0x03) << 4;
+        if (s.length > i + 1) {
+            groupsOfSix[1] |= s.charCodeAt(i + 1) >> 4;
+            groupsOfSix[2] = (s.charCodeAt(i + 1) & 0x0f) << 2;
+        }
+        if (s.length > i + 2) {
+            groupsOfSix[2] |= s.charCodeAt(i + 2) >> 6;
+            groupsOfSix[3] = s.charCodeAt(i + 2) & 0x3f;
+        }
+        for (var j = 0; j < groupsOfSix.length; j++) {
+            if (typeof groupsOfSix[j] == "undefined") {
+                out += "=";
+            } else {
+                out += btoaLookup(groupsOfSix[j]);
+            }
+        }
+    }
+    return out;
+}
+
+/**
+ * Lookup table for mybtoa(), which converts a six-bit number into the
+ * corresponding ASCII character.
+ */
+function btoaLookup(idx) {
+    if (idx < 26) {
+        return String.fromCharCode(idx + 'A'.charCodeAt(0));
+    }
+    if (idx < 52) {
+        return String.fromCharCode(idx - 26 + 'a'.charCodeAt(0));
+    }
+    if (idx < 62) {
+        return String.fromCharCode(idx - 52 + '0'.charCodeAt(0));
+    }
+    if (idx == 62) {
+        return '+';
+    }
+    if (idx == 63) {
+        return '/';
+    }
+    // Throw INVALID_CHARACTER_ERR exception here -- won't be hit in the tests.
+}
+
+function btoaException(input) {
+    input = String(input);
+    for (var i = 0; i < input.length; i++) {
+        if (input.charCodeAt(i) > 255) {
+            return true;
+        }
+    }
+    return false;
+}
+
+function testBtoa(input) {
+    // "The btoa() method must throw an INVALID_CHARACTER_ERR exception if the
+    // method's first argument contains any character whose code point is
+    // greater than U+00FF."
+    var normalizedInput = String(input);
+    for (var i = 0; i < normalizedInput.length; i++) {
+        if (normalizedInput.charCodeAt(i) > 255) {
+            assert_throws_dom("InvalidCharacterError", function() { btoa(input); },
+                "Code unit " + i + " has value " + normalizedInput.charCodeAt(i) + ", which is greater than 255");
+            return;
+        }
+    }
+    assert_equals(btoa(input), mybtoa(input));
+    assert_equals(atob(btoa(input)), String(input), "atob(btoa(input)) must be the same as String(input)");
+}
+
+var tests = ["עברית", "", "ab", "abc", "abcd", "abcde",
+    // This one is thrown in because IE9 seems to fail atob(btoa()) on it.  Or
+    // possibly to fail btoa().  I actually can't tell what's happening here,
+    // but it doesn't hurt.
+    "\xff\xff\xc0",
+    // Is your DOM implementation binary-safe?
+    "\0a", "a\0b",
+    // WebIDL tests.
+    undefined, null, 7, 12, 1.5, true, false, NaN, +Infinity, -Infinity, 0, -0,
+    {toString: function() { return "foo" }},
+];
+for (var i = 0; i < 258; i++) {
+    tests.push(String.fromCharCode(i));
+}
+tests.push(String.fromCharCode(10000));
+tests.push(String.fromCharCode(65534));
+tests.push(String.fromCharCode(65535));
+
+// This is supposed to be U+10000.
+tests.push(String.fromCharCode(0xd800, 0xdc00));
+tests = tests.map(
+    function(elem) {
+        var expected = mybtoa(elem);
+        if (expected === "INVALID_CHARACTER_ERR") {
+            return ["btoa("  + format_value(elem) + ") must raise INVALID_CHARACTER_ERR", elem];
+        }
+        return ["btoa(" + format_value(elem) + ") == " + format_value(mybtoa(elem)), elem];
+    }
+);
+
+var everything = "";
+for (var i = 0; i < 256; i++) {
+    everything += String.fromCharCode(i);
+}
+tests.push(["btoa(first 256 code points concatenated)", everything]);
+
+generate_tests(testBtoa, tests);
+
+promise_test(() => fetch("../../../fetch/data-urls/resources/base64.json").then(res => res.json()).then(runAtobTests), "atob() setup.");
+
+const idlTests = [
+  [undefined, null],
+  [null, [158, 233, 101]],
+  [7, null],
+  [12, [215]],
+  [1.5, null],
+  [true, [182, 187]],
+  [false, null],
+  [NaN, [53, 163]],
+  [+Infinity, [34, 119, 226, 158, 43, 114]],
+  [-Infinity, null],
+  [0, null],
+  [-0, null],
+  [{toString: function() { return "foo" }}, [126, 138]],
+  [{toString: function() { return "abcd" }}, [105, 183, 29]]
+];
+
+function runAtobTests(tests) {
+  const allTests = tests.concat(idlTests);
+  for(let i = 0; i < allTests.length; i++) {
+    const input = allTests[i][0],
+          output = allTests[i][1];
+    test(() => {
+      if(output === null) {
+        assert_throws_dom("InvalidCharacterError", () => globalThis.atob(input));
+      } else {
+        const result = globalThis.atob(input);
+        for(let ii = 0; ii < output.length; ii++) {
+          assert_equals(result.charCodeAt(ii), output[ii]);
+        }
+      }
+    }, "atob(" + format_value(input) + ")");
+  }
+}
diff --git a/test/fixtures/wpt/versions.json b/test/fixtures/wpt/versions.json
index 91bb213072cb925..07d4c70ebb0e0aa 100644
--- a/test/fixtures/wpt/versions.json
+++ b/test/fixtures/wpt/versions.json
@@ -1,23 +1,31 @@
 {
+  "common": {
+    "commit": "841a51412f236ad63655daca843d3b8e83e0777b",
+    "path": "common"
+  },
   "console": {
     "commit": "3b1f72e99a91d31551edd2147dc7b564eaf25d72",
     "path": "console"
   },
+  "dom/abort": {
+    "commit": "7caa3de7471cf19b78ee9efa313c7341a462b5e3",
+    "path": "dom/abort"
+  },
   "encoding": {
     "commit": "3c9820d1cc5d9d2627c26ef1268b6d54a35adf22",
     "path": "encoding"
   },
-  "url": {
-    "commit": "1783c9bccf48c426ec1017f36e1ccfcf90a8af47",
-    "path": "url"
+  "FileAPI": {
+    "commit": "3b279420d40afea32506e823f9ac005448f4f3d8",
+    "path": "FileAPI"
   },
-  "resources": {
-    "commit": "351a99782b9677706b5dc0dd78e85978fa4ab130",
-    "path": "resources"
+  "hr-time": {
+    "commit": "a5d1774ecf41751d1c9357c27c709ee33bf3e279",
+    "path": "hr-time"
   },
-  "interfaces": {
-    "commit": "b4be9a3fdf18459a924f88e49bc55d8b30faa93a",
-    "path": "interfaces"
+  "html/webappapis/atob": {
+    "commit": "f267e1dca6f57a9f4d69f32a6920adfdb3268656",
+    "path": "html/webappapis/atob"
   },
   "html/webappapis/microtask-queuing": {
     "commit": "2c5c3c4c27d27a419c1fdba3e9879c2d22037074",
@@ -27,20 +35,16 @@
     "commit": "264f12bc7bf5db0c6dd064842a5d39ccbf9208c5",
     "path": "html/webappapis/timers"
   },
-  "hr-time": {
-    "commit": "a5d1774ecf41751d1c9357c27c709ee33bf3e279",
-    "path": "hr-time"
-  },
-  "common": {
-    "commit": "841a51412f236ad63655daca843d3b8e83e0777b",
-    "path": "common"
+  "interfaces": {
+    "commit": "b4be9a3fdf18459a924f88e49bc55d8b30faa93a",
+    "path": "interfaces"
   },
-  "dom/abort": {
-    "commit": "7caa3de7471cf19b78ee9efa313c7341a462b5e3",
-    "path": "dom/abort"
+  "resources": {
+    "commit": "351a99782b9677706b5dc0dd78e85978fa4ab130",
+    "path": "resources"
   },
-  "FileAPI": {
-    "commit": "3b279420d40afea32506e823f9ac005448f4f3d8",
-    "path": "FileAPI"
+  "url": {
+    "commit": "1783c9bccf48c426ec1017f36e1ccfcf90a8af47",
+    "path": "url"
   }
 }
\ No newline at end of file
diff --git a/test/wpt/status/html/webappapis/atob.json b/test/wpt/status/html/webappapis/atob.json
new file mode 100644
index 000000000000000..0967ef424bce679
--- /dev/null
+++ b/test/wpt/status/html/webappapis/atob.json
@@ -0,0 +1 @@
+{}
diff --git a/test/wpt/test-atob.js b/test/wpt/test-atob.js
new file mode 100644
index 000000000000000..51fa27e36d3f2f0
--- /dev/null
+++ b/test/wpt/test-atob.js
@@ -0,0 +1,19 @@
+'use strict';
+
+require('../common');
+const { WPTRunner } = require('../common/wpt');
+
+const runner = new WPTRunner('html/webappapis/atob');
+
+// Needed to access to DOMException.
+runner.setFlags(['--expose-internals']);
+
+// Set a script that will be executed in the worker before running the tests.
+runner.setInitScript(`
+  const { internalBinding } = require('internal/test/binding');
+  const { atob, btoa } = require('buffer');
+  const { DOMException } = internalBinding('messaging');
+  global.DOMException = DOMException;
+`);
+
+runner.runJsTests();