diff --git a/.circleci/config.yml b/.circleci/config.yml
index 91c281e7118..6746f8e7bf0 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -3,7 +3,7 @@ version: 2
 jobs:
   build:
     docker:
-      - image: circleci/node:12
+      - image: circleci/node:12-browsers
     steps:
       - checkout
       - run:
diff --git a/packages/opentelemetry-core/karma.conf.js b/packages/opentelemetry-core/karma.conf.js
new file mode 100644
index 00000000000..4066eae7cd3
--- /dev/null
+++ b/packages/opentelemetry-core/karma.conf.js
@@ -0,0 +1,31 @@
+/**
+ * Copyright 2019, OpenTelemetry Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+const webpackConfig = require('./webpack/test.config.js');
+
+module.exports = (config) => {
+  config.set({
+    listenAddress: 'localhost',
+    hostname: 'localhost',
+    browsers: ['ChromeHeadless'],
+    frameworks: ['mocha'],
+    reporters: ['spec'],
+    files: ['test/index-webpack.ts'],
+    preprocessors: {'test/index-webpack.ts': ['webpack']},
+    webpack: webpackConfig,
+    webpackMiddleware: {noInfo: true},
+  });
+};
diff --git a/packages/opentelemetry-core/package.json b/packages/opentelemetry-core/package.json
index 2be955b0051..dff2afcad55 100644
--- a/packages/opentelemetry-core/package.json
+++ b/packages/opentelemetry-core/package.json
@@ -3,11 +3,18 @@
   "version": "0.0.1",
   "description": "OpenTelemetry Core",
   "main": "build/src/index.js",
+  "browser": {
+    "./src/platform/index.ts": "./src/platform/browser/index.ts"
+  },
   "types": "build/src/index.d.ts",
   "repository": "open-telemetry/opentelemetry-js",
   "scripts": {
-    "test": "nyc ts-mocha -p tsconfig.json test/**/*.ts",
-    "tdd": "yarn test -- --watch-extensions ts --watch",
+    "test": "yarn test:node && yarn test:browser",
+    "test:node": "nyc ts-mocha -p tsconfig.json test/**/*.ts",
+    "test:browser": "karma start --single-run",
+    "tdd": "yarn tdd:node",
+    "tdd:node": "yarn test -- --watch-extensions ts --watch",
+    "tdd:browser": "karma start",
     "codecov": "nyc report --reporter=json && codecov -f coverage/*.json",
     "clean": "rimraf build/*",
     "check": "gts check",
@@ -40,9 +47,13 @@
       ".ts"
     ],
     "exclude": [
-      "src/index.ts",
       "**/*.d.ts",
-      "build/**/**/*.js"
+      "build/**/**/*.js",
+      "karma.conf.js",
+      "src/index.ts",
+      "src/platform/browser/*.ts",
+      "test/index-webpack.ts",
+      "webpack/*.js"
     ],
     "all": true
   },
@@ -52,12 +63,20 @@
   "devDependencies": {
     "@types/mocha": "^5.2.5",
     "@types/node": "^10.12.12",
+    "@types/webpack-env": "1.13.9",
     "codecov": "^3.1.0",
     "gts": "^1.0.0",
+    "karma": "^4.1.0",
+    "karma-chrome-launcher": "^2.2.0",
+    "karma-mocha": "^1.3.0",
+    "karma-spec-reporter": "^0.0.32",
+    "karma-webpack": "^4.0.2",
     "mocha": "^6.1.0",
     "nyc": "^14.0.0",
+    "ts-loader": "^6.0.4",
     "ts-mocha": "^6.0.0",
     "ts-node": "^8.0.0",
+    "webpack": "^4.35.2",
     "typescript": "^3.4.5"
   },
   "dependencies": {
diff --git a/packages/opentelemetry-core/src/platform/browser/id.ts b/packages/opentelemetry-core/src/platform/browser/id.ts
new file mode 100644
index 00000000000..11038e010f6
--- /dev/null
+++ b/packages/opentelemetry-core/src/platform/browser/id.ts
@@ -0,0 +1,44 @@
+/**
+ * Copyright 2019, OpenTelemetry Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// IE 11 exposes `crypto` as `msCrypto`.
+declare type WindowWithMsCrypto = Window & {
+  msCrypto?: Crypto;
+};
+const cryptoLib = window.crypto || (window as WindowWithMsCrypto).msCrypto;
+
+const SPAN_ID_BYTES = 8;
+const spanBytesArray = new Uint8Array(SPAN_ID_BYTES);
+
+/** Returns a random 16-byte trace ID formatted as a 32-char hex string. */
+export function randomTraceId(): string {
+  return randomSpanId() + randomSpanId();
+}
+
+/** Returns a random 8-byte span ID formatted as a 16-char hex string. */
+export function randomSpanId(): string {
+  let spanId = '';
+  cryptoLib.getRandomValues(spanBytesArray);
+  for (let i = 0; i < SPAN_ID_BYTES; i++) {
+    const hexStr = spanBytesArray[i].toString(16);
+
+    // Zero pad bytes whose hex values are single digit.
+    if (hexStr.length === 1) spanId += '0';
+
+    spanId += hexStr;
+  }
+  return spanId;
+}
diff --git a/packages/opentelemetry-core/src/platform/browser/index.ts b/packages/opentelemetry-core/src/platform/browser/index.ts
new file mode 100644
index 00000000000..048ff30c5a7
--- /dev/null
+++ b/packages/opentelemetry-core/src/platform/browser/index.ts
@@ -0,0 +1,17 @@
+/**
+ * Copyright 2019, OpenTelemetry Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+export * from './id';
diff --git a/packages/opentelemetry-core/src/platform/index.ts b/packages/opentelemetry-core/src/platform/index.ts
new file mode 100644
index 00000000000..7a0ffcb5018
--- /dev/null
+++ b/packages/opentelemetry-core/src/platform/index.ts
@@ -0,0 +1,20 @@
+/**
+ * Copyright 2019, OpenTelemetry Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// Use the node platform by default. The "browser" field of package.json is used
+// to override this file to use `./browser/index.ts` when packaged with
+// webpack, Rollup, etc.
+export * from './node';
diff --git a/packages/opentelemetry-core/src/common/util/id.ts b/packages/opentelemetry-core/src/platform/node/id.ts
similarity index 100%
rename from packages/opentelemetry-core/src/common/util/id.ts
rename to packages/opentelemetry-core/src/platform/node/id.ts
diff --git a/packages/opentelemetry-core/src/platform/node/index.ts b/packages/opentelemetry-core/src/platform/node/index.ts
new file mode 100644
index 00000000000..048ff30c5a7
--- /dev/null
+++ b/packages/opentelemetry-core/src/platform/node/index.ts
@@ -0,0 +1,17 @@
+/**
+ * Copyright 2019, OpenTelemetry Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+export * from './id';
diff --git a/packages/opentelemetry-core/test/index-webpack.ts b/packages/opentelemetry-core/test/index-webpack.ts
new file mode 100644
index 00000000000..a1b2c077f62
--- /dev/null
+++ b/packages/opentelemetry-core/test/index-webpack.ts
@@ -0,0 +1,20 @@
+/**
+ * Copyright 2019, OpenTelemetry Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// This file is the webpack entry point for the browser Karma tests. It requires
+// all modules ending in "test" from the current folder and all its subfolders.
+const testsContext = require.context('.', true, /test$/);
+testsContext.keys().forEach(testsContext);
diff --git a/packages/opentelemetry-core/test/common/util.id.test.ts b/packages/opentelemetry-core/test/platform/id.test.ts
similarity index 93%
rename from packages/opentelemetry-core/test/common/util.id.test.ts
rename to packages/opentelemetry-core/test/platform/id.test.ts
index bfaec6e74e3..a38aec7b4ec 100644
--- a/packages/opentelemetry-core/test/common/util.id.test.ts
+++ b/packages/opentelemetry-core/test/platform/id.test.ts
@@ -15,7 +15,7 @@
  */
 
 import * as assert from 'assert';
-import { randomSpanId, randomTraceId } from '../../src/common/util/id';
+import { randomSpanId, randomTraceId } from '../../src/platform';
 
 describe('randomTraceId', () => {
   it('returns different 32-char hex strings', () => {
diff --git a/packages/opentelemetry-core/webpack/test.config.js b/packages/opentelemetry-core/webpack/test.config.js
new file mode 100644
index 00000000000..1a3ef4e3086
--- /dev/null
+++ b/packages/opentelemetry-core/webpack/test.config.js
@@ -0,0 +1,86 @@
+/**
+ * Copyright 2019, OpenTelemetry Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// This is the webpack configuration for browesr Karma tests.
+module.exports = {
+  mode: 'development',
+  output: {filename: 'bundle.js'},
+  resolve: {extensions: ['.ts', '.js']},
+  devtool: 'inline-source-map',
+  module: {
+    rules: [
+      {test: /\.ts$/, use: 'ts-loader'},
+      {
+        parser: {
+          // This setting configures Node polyfills for the browser that will be
+          // added to the webpack bundle for Karma tests.
+          node: {
+            // Enable the assert library polyfill because that is used in tests
+            assert: true,
+            // The assert polyfill from github.com/browserify/commonjs-assert
+            // also requires the `global` polyfill.
+            global: true,
+
+            // Turn off all other Node.js API polyfills for the browser tests to
+            // make sure that we are not attempting to use Node-specific APIs in
+            // the browser code. Instead, we will write browser specific
+            // implementations of platform functionality we need under the
+            // `./src/platform/browser` folder. This allows for writing browser
+            // optimized implementations of the specific needed functionality
+            // rather than bringing in (sometimes large) polyfills for the
+            // corresponding Node APIs.
+            Buffer: false,
+            __dirname: false,
+            __filename: false,
+            buffer: false,
+            child_process: false,
+            cluster: false,
+            console: false,
+            constants: false,
+            crypto: false,
+            dgram: false,
+            dns: false,
+            domain: false,
+            events: false,
+            fs: false,
+            http: false,
+            https: false,
+            module: false,
+            net: false,
+            os: false,
+            path: false,
+            process: false,
+            punycode: false,
+            querystring: false,
+            readline: false,
+            repl: false,
+            setImmediate: false,
+            stream: false,
+            string_decoder: false,
+            sys: false,
+            timers: false,
+            tls: false,
+            tty: false,
+            url: false,
+            util: false,
+            vm: false,
+            zlib: false,
+          },
+        },
+      },
+    ],
+  },
+};