diff --git a/.gitignore b/.gitignore
index 13b8318be2..cbbc6f3b88 100644
--- a/.gitignore
+++ b/.gitignore
@@ -13,6 +13,7 @@ typings/
 # Generated
 dist/
 .tshy-build
+.wpt
 
 # Import location artifacts
 packages/rxjs/ajax/
diff --git a/packages/observable/.npmignore b/packages/observable/.npmignore
new file mode 100644
index 0000000000..2c440e812a
--- /dev/null
+++ b/packages/observable/.npmignore
@@ -0,0 +1,2 @@
+# Ignore spec files
+dist/**/*.spec.*
\ No newline at end of file
diff --git a/packages/observable/package.json b/packages/observable/package.json
index e296727097..8a9e907c9c 100644
--- a/packages/observable/package.json
+++ b/packages/observable/package.json
@@ -17,7 +17,8 @@
     "build": "tshy",
     "lint": "eslint ./src",
     "test": "vitest --run",
-    "test:watch": "vitest"
+    "test:watch": "vitest",
+    "test:wpt": "node ./scripts/web-platform-tests.mjs"
   },
   "repository": {
     "type": "git",
diff --git a/packages/observable/scripts/web-platform-tests.mjs b/packages/observable/scripts/web-platform-tests.mjs
new file mode 100644
index 0000000000..500400e6db
--- /dev/null
+++ b/packages/observable/scripts/web-platform-tests.mjs
@@ -0,0 +1,220 @@
+import { spawn } from 'node:child_process';
+import fs from 'node:fs';
+import path from 'node:path';
+
+const testPath = 'dom/observable/tentative';
+
+const __filename = new URL(import.meta.url).pathname;
+const __dirname = path.dirname(__filename);
+
+const wptDir = path.join(__dirname, '.wpt');
+const polyfillScriptPath = path.resolve(__dirname, '../dist/esm/polyfill.js');
+
+console.log(bold(wptDir));
+
+function runCommand(command, args = [], options = {}) {
+  return new Promise((resolve, reject) => {
+    // We also want to make sure we log the output from the subprocess
+    const subprocess = spawn(command, args, { stdio: 'inherit', ...options });
+
+    subprocess.on('close', (code) => {
+      if (code === 0) {
+        resolve();
+      } else {
+        reject(new Error(`Command failed with exit code ${code}: ${command} ${args.join(' ')}`));
+      }
+    });
+
+    // Log output from the subprocess
+    subprocess.stdout?.on('data', (data) => {
+      console.log(data.toString());
+    });
+
+    subprocess.stderr?.on('data', (data) => {
+      console.error(data.toString());
+    });
+
+    // Be sure that if the main process is killed, the subprocess is also killed
+    process.on('SIGINT', () => {
+      if (subprocess.exitCode === null) subprocess.kill();
+    });
+  });
+}
+
+/**
+ * Uses git to clone the WPT repository into the .wpt directory
+ * if it doesn't already exist.
+ *
+ * If it does exist, it pulls the latest changes.
+ */
+async function ensureWPTRepo() {
+  if (!fs.existsSync(wptDir)) {
+    console.log('Cloning WPT repository...');
+    await runCommand('git', ['clone', 'https://github.com/web-platform-tests/wpt.git', wptDir]);
+  } else {
+    console.log('WPT repository already exists. Pulling latest changes...');
+    await runCommand('git', ['pull'], { cwd: wptDir });
+  }
+}
+
+let unhandledErrors = null;
+
+process.on('unhandledRejection', (error) => {
+  unhandledErrors ??= [];
+  unhandledErrors.push(error);
+});
+
+process.on('uncaughtException', (error) => {
+  unhandledErrors ??= [];
+  unhandledErrors.push(error);
+});
+
+const testHarnessScriptPath = path.join(wptDir, 'resources', 'testharness.js');
+const testHarnessScript = fs.readFileSync(testHarnessScriptPath, 'utf8');
+
+let _self;
+let _window;
+let _addEventListener;
+let _removeEventListener;
+let _dispatchEvent;
+
+function beforeEach() {
+  unhandledErrors = null;
+  _self = globalThis.self;
+  _window = globalThis.window;
+  _addEventListener = globalThis.addEventListener;
+  _removeEventListener = globalThis.removeEventListener;
+  _dispatchEvent = globalThis.dispatchEvent;
+
+  globalThis.window = globalThis.self = globalThis;
+
+  if (typeof globalThis.addEventListener !== 'function') {
+    const globalEventTarget = new EventTarget();
+    globalThis.addEventListener = (...args) => {
+      globalEventTarget.addEventListener(...args);
+    };
+    globalThis.removeEventListener = (...args) => {
+      globalEventTarget.removeEventListener(...args);
+    };
+    globalThis.dispatchEvent = (...args) => {
+      globalEventTarget.dispatchEvent(...args);
+    };
+  }
+}
+
+function getUnhandledErrors() {
+  return new Promise((resolve) => {
+    setTimeout(() => {
+      resolve(unhandledErrors);
+    });
+  });
+}
+
+function afterEach() {
+  globalThis.self = _self;
+  globalThis.window = _window;
+  globalThis.addEventListener = _addEventListener;
+  globalThis.removeEventListener = _removeEventListener;
+  globalThis.dispatchEvent = _dispatchEvent;
+}
+
+function initializeTestHarness() {
+  const execute = new Function(testHarnessScript);
+  execute();
+}
+
+async function executeTest(test) {
+  beforeEach();
+  try {
+    initializeTestHarness();
+    const testComplete = new Promise((resolve) => {
+      add_completion_callback((tests, status) => {
+        resolve({ tests, status });
+      });
+    });
+    await import(path.join(wptDir, testPath, test));
+
+    const unhandledErrors = await getUnhandledErrors();
+    const result = await testComplete;
+
+    return { ...result, unhandledErrors };
+  } finally {
+    afterEach();
+  }
+}
+
+async function* runTests() {
+  const tests = await fs.promises.readdir(path.join(wptDir, testPath));
+  const validTests = tests.filter((test) => test.endsWith('.any.js'));
+  for (let test of validTests) {
+    yield { test, result: await executeTest(test) };
+  }
+}
+
+function prettyPrintTestResult({ test, result }) {
+  console.log(`\n${bold(test)}:`);
+  if (result.unhandledErrors) {
+    console.log(red('Unhandled errors:'));
+    for (const error of result.unhandledErrors) {
+      console.error(error);
+    }
+  }
+
+  for (const test of result.tests) {
+    if (test.status === 0) {
+      console.log(green('PASS'), test.name);
+    } else {
+      console.log(red('FAIL'), test.name);
+      console.log(test.message);
+    }
+  }
+}
+
+async function main() {
+  await import(polyfillScriptPath);
+
+  await ensureWPTRepo();
+
+  let totalTests = 0;
+  let totalFailed = 0;
+  let hadUnhandledErrors = false;
+
+  for await (const testResult of runTests()) {
+    totalTests += testResult.result.tests.length;
+    totalFailed += testResult.result.tests.filter((test) => test.status !== 0).length;
+    if (testResult.result.unhandledErrors) {
+      hadUnhandledErrors = true;
+    }
+
+    prettyPrintTestResult(testResult);
+  }
+
+  console.log();
+  console.log(bold('Summary:'));
+  console.log(bold(`Total tests: ${totalTests}`));
+  console.log(bold(`Failed: ${totalFailed}`));
+  console.log(bold(`Unhandled errors: ${hadUnhandledErrors ? 'yes' : 'no'}`));
+  console.log();
+
+  if (hadUnhandledErrors || totalFailed > 0) {
+    process.exit(1);
+  }
+}
+
+main();
+
+function color(text, color) {
+  return `\x1b[${color}m${text}\x1b[0m`;
+}
+
+function red(text) {
+  return color(text, 31);
+}
+
+function bold(text) {
+  return color(text, 1);
+}
+
+function green(text) {
+  return color(text, 32);
+}
diff --git a/packages/observable/src/observable.ts b/packages/observable/src/observable.ts
index 31f8403d15..926a67cdb8 100644
--- a/packages/observable/src/observable.ts
+++ b/packages/observable/src/observable.ts
@@ -238,7 +238,7 @@ export interface SubscriberOverrides<T> {
  */
 export class Subscriber<T> extends Subscription implements Observer<T> {
   /** @internal */
-  protected isStopped: boolean = false;
+  protected isStopped = false;
   /** @internal */
   protected destination: Observer<T>;
 
diff --git a/packages/observable/src/polyfill.ts b/packages/observable/src/polyfill.ts
new file mode 100644
index 0000000000..969d99c2d5
--- /dev/null
+++ b/packages/observable/src/polyfill.ts
@@ -0,0 +1,13 @@
+import { Observable } from './observable.js';
+
+// get the global variable so we can polyfill Observable on it
+// the environment may be a web worker, Node.js, or a browser
+// we need to use the correct global context
+
+const _globalThis = typeof globalThis !== 'undefined' ? globalThis : typeof self !== 'undefined' ? self : global;
+
+// @ts-expect-error we're adding a property to the global object here
+if (typeof _globalThis.Observable !== 'function') {
+  // @ts-expect-error we're adding a property to the global object here
+  _globalThis.Observable = Observable;
+}