diff --git a/archive/compress.js b/archive/compress.js
new file mode 100644
index 0000000..1a72ee2
--- /dev/null
+++ b/archive/compress.js
@@ -0,0 +1,130 @@
+
+import { ByteBuffer } from '../io/bytebuffer.js';
+
+// NOTE: THIS IS A VERY HACKY WORK-IN-PROGRESS! THE API IS NOT FROZEN! USE AT YOUR OWN RISK!
+
+/**
+ * @typedef FileInfo An object that is sent to the worker to represent a file to zip.
+ * @property {string} fileName The name of the file. TODO: Includes the path?
+ * @property {number} lastModTime The number of ms since the Unix epoch (1970-01-01 at midnight).
+ * @property {ArrayBuffer} fileData The bytes of the file.
+ */
+
+/**
+ * @typedef CompressorOptions
+ * @property {string} pathToBitJS A string indicating where the BitJS files are located.
+ */
+
+/**
+ * @readonly
+ * @enum {string}
+ */
+export const CompressStatus = {
+  NOT_STARTED: 'not_started',
+  READY: 'ready',
+  WORKING: 'working',
+  COMPLETE: 'complete',
+  ERROR: 'error',
+};
+
+/**
+ * A thing that zips files.
+ * NOTE: THIS IS A VERY HACKY WORK-IN-PROGRESS! THE API IS NOT FROZEN! USE AT YOUR OWN RISK!
+ */
+export class Zipper {
+  /**
+   * @param {CompressorOptions} options
+   */
+  constructor(options) {
+    /**
+     * The path to the BitJS files.
+     * @type {string}
+     * @private
+     */
+    this.pathToBitJS = options.pathToBitJS || '/';
+
+    /**
+     * Private web worker initialized during start().
+     * @type {Worker}
+     * @private
+     */
+    this.worker_ = null;
+
+    /**
+     * @type {CompressStatus}
+     * @private
+     */
+    this.compressState = CompressStatus.NOT_STARTED;
+
+    /**
+     * @type {Uint8Array}
+     * @private
+     */
+    this.byteArray = new Uint8Array(0);
+  }
+
+  /**
+   * Must only be called on a Zipper that has been started. See start().
+   * @param {FileInfo[]} files 
+   * @param {boolean} isLastFile 
+   */
+  appendFiles(files, isLastFile) {
+    if (!this.worker_) {
+      throw `Worker not initialized. Did you forget to call start() ?`;
+    }
+    if (![CompressStatus.READY, CompressStatus.WORKING].includes(this.compressState)) {
+      throw `Zipper not in the right state: ${this.compressState}`;
+    }
+
+    this.worker_.postMessage({ files, isLastFile });
+  }
+
+  /**
+   * @param {FileInfo[]} files
+   * @param {boolean} isLastFile
+   * @returns {Promise<Uint8Array>} A Promise that contains the entire zipped archive.
+   */
+  start(files, isLastFile) {
+    return new Promise((resolve, reject) => {
+      this.worker_ = new Worker(this.pathToBitJS + `archive/zip.js`);
+      this.worker_.onerror = (evt) => {
+        console.log('Worker error: message = ' + evt.message);
+        throw evt.message;
+      };
+      this.worker_.onmessage = (evt) => {
+        if (typeof evt.data == 'string') {
+          // Just log any strings the worker pumps our way.
+          console.log(evt.data);
+        } else {
+          switch (evt.data.type) {
+            case 'start':
+              this.compressState = CompressStatus.WORKING;
+              break;
+            case 'finish':
+              this.compressState = CompressStatus.COMPLETE;
+              resolve(this.byteArray);
+              break;
+            case 'compress':
+              this.addBytes_(evt.data.bytes);
+              break;
+          }
+        }
+      };
+
+      this.compressState = CompressStatus.READY;
+      this.appendFiles(files, isLastFile);
+    });
+  }
+
+  /**
+   * Updates the internal byte array with new bytes (by allocating a new array and copying).
+   * @param {Uint8Array} newBytes
+   * @private
+   */
+  addBytes_(newBytes) {
+    const oldArray = this.byteArray;
+    this.byteArray = new Uint8Array(oldArray.byteLength + newBytes.byteLength);
+    this.byteArray.set(oldArray);
+    this.byteArray.set(newBytes, oldArray.byteLength);
+  }
+}
\ No newline at end of file
diff --git a/archive/unzip.js b/archive/unzip.js
index d6c9608..166ed6d 100644
--- a/archive/unzip.js
+++ b/archive/unzip.js
@@ -73,7 +73,9 @@ const BIT = [0x01, 0x02, 0x04, 0x08,
   0x1000, 0x2000, 0x4000, 0x8000];
 
 class ZipLocalFile {
-  // takes a ByteStream and parses out the local file information
+  /**
+   * @param {bitjs.io.ByteStream} bstream 
+   */
   constructor(bstream) {
     if (typeof bstream != typeof {} || !bstream.readNumber || typeof bstream.readNumber != typeof function () { }) {
       return null;
@@ -734,7 +736,6 @@ onmessage = function (event) {
     bytestream = new bitjs.io.ByteStream(bytes);
   } else {
     bytestream.push(bytes);
-    // TODO: Shouldn't this return here if it's not waiting?
   }
 
   if (unarchiveState === UnarchiveState.NOT_STARTED) {
diff --git a/archive/zip.js b/archive/zip.js
new file mode 100644
index 0000000..701466e
--- /dev/null
+++ b/archive/zip.js
@@ -0,0 +1,235 @@
+/**
+ * zip.js
+ *
+ * Licensed under the MIT License
+ *
+ * Copyright(c) 2021 Google Inc.
+ *
+ * Reference Documentation:
+ *
+ * ZIP format: http://www.pkware.com/documents/casestudies/APPNOTE.TXT
+ * DEFLATE format: http://tools.ietf.org/html/rfc1951
+ */
+
+// This file expects to be invoked as a Worker (see onmessage below).
+importScripts('../io/bitstream-worker.js');
+importScripts('../io/bytebuffer-worker.js');
+importScripts('../io/bytestream-worker.js');
+
+/**
+ * The client sends messages to this Worker containing files to archive in order. The client
+ * indicates to the Worker when the last file has been sent to be compressed.
+ *
+ * The Worker emits an event to indicate compression has started: { type: 'start' }
+ * As the files compress, bytes are sent back in order: { type: 'compress', bytes: Uint8Array }
+ * After the last file compresses, the Worker indicates finish by: { type 'finish' }
+ *
+ * Clients should append the bytes to a single buffer in the order they were received.
+ */
+
+/**
+ * @typedef FileInfo An object that is sent to this worker by the client to represent a file.
+ * @property {string} fileName The name of this file. TODO: Includes the path?
+ * @property {number} lastModTime The number of ms since the Unix epoch (1970-01-01 at midnight).
+ * @property {Uint8Array} fileData The raw bytes of the file.
+ */
+
+// TODO: Support DEFLATE.
+// TODO: Support options that can let client choose levels of compression/performance.
+
+/**
+ * Ideally these constants should be defined in a common isomorphic ES module. Unfortunately, the
+ * state of JavaScript is such that modules cannot be shared easily across browsers, worker threads,
+ * NodeJS environments, etc yet. Thus, these constants, as well as logic that should be extracted to
+ * common modules and shared with unzip.js are not yet easily possible.
+ */
+
+const zLocalFileHeaderSignature = 0x04034b50;
+const zCentralFileHeaderSignature = 0x02014b50;
+const zEndOfCentralDirSignature = 0x06054b50;
+
+/**
+ * @typedef CentralDirectoryFileHeaderInfo An object to be used to construct the central directory.
+ * @property {string} fileName
+ * @property {number} compressionMethod (2 bytes)
+ * @property {number} lastModFileTime (2 bytes)
+ * @property {number} lastModFileDate (2 bytes)
+ * @property {number} crc32 (4 bytes)
+ * @property {number} compressedSize (4 bytes)
+ * @property {number} uncompressedSize (4 bytes)
+ * @property {number} byteOffset (4 bytes)
+ */
+
+/** @type {FileInfo[]} */
+let filesCompressed = [];
+
+/** @type {CentralDirectoryFileHeaderInfo[]} */
+let centralDirectoryInfos = [];
+
+/** @type {number} */
+let numBytesWritten = 0;
+
+const CompressorState = {
+  NOT_STARTED: 0,
+  COMPRESSING: 1,
+  WAITING: 2,
+  FINISHED: 3,
+};
+let state = CompressorState.NOT_STARTED;
+let lastFileReceived = false;
+
+/** Helper functions. */
+
+/**
+ * Logic taken from https://github.com/thejoshwolfe/yazl.
+ * @param {number} lastModTime The number of ms since the Unix epoch (1970-01-01 at midnight).
+ * @returns {number}
+ */
+function dateToDosDate(jsDate) {
+  let date = 0;
+  date |= jsDate.getDate() & 0x1f; // 1-31
+  date |= ((jsDate.getMonth() + 1) & 0xf) << 5; // 0-11, 1-12
+  date |= ((jsDate.getFullYear() - 1980) & 0x7f) << 9; // 0-128, 1980-2108
+  return date;
+}
+
+/**
+ * Logic taken from https://github.com/thejoshwolfe/yazl.
+ * @param {number} lastModTime The number of ms since the Unix epoch (1970-01-01 at midnight).
+ * @returns {number}
+ */
+function dateToDosTime(jsDate) {
+  let time = 0;
+  time |= Math.floor(jsDate.getSeconds() / 2); // 0-59, 0-29 (lose odd numbers)
+  time |= (jsDate.getMinutes() & 0x3f) << 5; // 0-59
+  time |= (jsDate.getHours() & 0x1f) << 11; // 0-23
+  return time;
+}
+
+/**
+ * @param {FileInfo} file
+ * @returns {bitjs.io.ByteBuffer}
+ */
+function zipOneFile(file) {
+  // Zip Local File Header has 30 bytes and then the filename and extrafields.
+  const fileHeaderSize = 30 + file.fileName.length;
+
+  /** @type {bitjs.io.ByteBuffer} */
+  const buffer = new bitjs.io.ByteBuffer(fileHeaderSize + file.fileData.length);
+
+  buffer.writeNumber(zLocalFileHeaderSignature, 4); // Magic number.
+  buffer.writeNumber(0x0A, 2); // Version.
+  buffer.writeNumber(0, 2); // General Purpose Flags.
+  buffer.writeNumber(0, 2); // Compression Method. 0 = Store only.
+
+  const jsDate = new Date(file.lastModTime);
+
+  /** @type {CentralDirectoryFileHeaderInfo} */
+  const centralDirectoryInfo = {
+    compressionMethod: 0,
+    lastModFileTime: dateToDosTime(jsDate),
+    lastModFileDate: dateToDosDate(jsDate),
+    // TODO: Calculate. See section 4.4.7 of https://pkware.cachefly.net/webdocs/casestudies/APPNOTE.TXT.
+    crc32: 0,
+    // TODO: For now, this is easy. Later when we do DEFLATE, we will have to calculate.
+    compressedSize: file.fileData.byteLength,
+    uncompressedSize: file.fileData.byteLength,
+    fileName: file.fileName,
+    byteOffset: numBytesWritten,
+  };
+  centralDirectoryInfos.push(centralDirectoryInfo);
+
+  buffer.writeNumber(centralDirectoryInfo.lastModFileTime, 2); // Last Mod File Time.
+  buffer.writeNumber(centralDirectoryInfo.lastModFileDate, 2); // Last Mod Date.
+  buffer.writeNumber(centralDirectoryInfo.crc32, 4); // crc32.
+  buffer.writeNumber(centralDirectoryInfo.compressedSize, 4); // Compressed size.
+  buffer.writeNumber(centralDirectoryInfo.uncompressedSize, 4); // Uncompressed size.
+  buffer.writeNumber(centralDirectoryInfo.fileName.length, 2); // Filename length.
+  buffer.writeNumber(0, 2); // Extra field length.
+  buffer.writeASCIIString(centralDirectoryInfo.fileName); // Filename. Assumes ASCII.
+  buffer.insertBytes(file.fileData); // File data.
+
+  return buffer;
+}
+
+/**
+ * @returns {bitjs.io.ByteBuffer}
+ */
+function writeCentralFileDirectory() {
+  // Each central directory file header is 46 bytes + the filename.
+  let filenameLengths = filesCompressed.map(f => f.fileName.length).reduce((acc, cur) => acc + cur);
+  const sizeOfCentralDirectoryEntries = (filesCompressed.length * 46) + filenameLengths;
+
+  const buffer = new bitjs.io.ByteBuffer(sizeOfCentralDirectoryEntries + 22);
+
+  for (const cdInfo of centralDirectoryInfos) {
+    buffer.writeNumber(zCentralFileHeaderSignature, 4); // Magic number.
+    buffer.writeNumber(0, 2); // Version made by. // 0x31e
+    buffer.writeNumber(0, 2); // Version needed to extract (minimum). // 0x14
+    buffer.writeNumber(0, 2); // General purpose bit flag
+    buffer.writeNumber(0, 2); // Compression method.
+    buffer.writeNumber(cdInfo.lastModFileTime, 2); // Last Mod File Time.
+    buffer.writeNumber(cdInfo.lastModFileDate, 2); // Last Mod Date.
+    buffer.writeNumber(cdInfo.crc32, 4); // crc32.
+    buffer.writeNumber(cdInfo.compressedSize, 4); // Compressed size.
+    buffer.writeNumber(cdInfo.uncompressedSize, 4); // Uncompressed size.
+    buffer.writeNumber(cdInfo.fileName.length, 2); // File name length.
+    buffer.writeNumber(0, 2); // Extra field length.
+    buffer.writeNumber(0, 2); // Comment length.
+    buffer.writeNumber(0, 2); // Disk number where file starts.
+    buffer.writeNumber(0, 2); // Internal file attributes.
+    buffer.writeNumber(0, 4); // External file attributes.
+    buffer.writeNumber(cdInfo.byteOffset, 4); // Relative offset of local file header.
+    buffer.writeASCIIString(cdInfo.fileName); // File name.
+  }
+
+  // 22 more bytes.
+  buffer.writeNumber(zEndOfCentralDirSignature, 4); // Magic number.
+  buffer.writeNumber(0, 2); // Number of this disk.
+  buffer.writeNumber(0, 2); // Disk where central directory starts.
+  buffer.writeNumber(filesCompressed.length, 2); // Number of central directory records on this disk.
+  buffer.writeNumber(filesCompressed.length, 2); // Total number of central directory records.
+  buffer.writeNumber(sizeOfCentralDirectoryEntries, 4); // Size of central directory.
+  buffer.writeNumber(numBytesWritten, 4); // Offset of start of central directory.
+  buffer.writeNumber(0, 2); // Comment length.
+
+  return buffer;
+}
+
+/**
+ * @param {{data: {isLastFile?: boolean, files: FileInfo[]}}} evt The event for the Worker
+ *     to process. It is an error to send any more events to the Worker if a previous event had
+ *     isLastFile is set to true.
+ */
+onmessage = function(evt) {
+  if (state === CompressorState.FINISHED) {
+    throw `The zip worker was sent a message after last file received.`;
+  }
+
+  if (state === CompressorState.NOT_STARTED) {
+    postMessage({ type: 'start' });
+  }
+
+  state = CompressorState.COMPRESSING;
+
+  /** @type {FileInfo[]} */
+  const filesToCompress = evt.data.files;
+  while (filesToCompress.length > 0) {
+    const fileInfo = filesToCompress.shift();
+    const fileBuffer = zipOneFile(fileInfo);
+    filesCompressed.push(fileInfo);
+    numBytesWritten += fileBuffer.data.byteLength;
+    this.postMessage({ type: 'compress', bytes: fileBuffer.data }, [ fileBuffer.data.buffer ]);
+  }
+
+  if (evt.data.isLastFile) {
+    const centralBuffer = writeCentralFileDirectory();
+    numBytesWritten += centralBuffer.data.byteLength;
+    this.postMessage({ type: 'compress', bytes: centralBuffer.data }, [ centralBuffer.data.buffer ]);
+
+    state = CompressorState.FINISHED;
+    this.postMessage({ type: 'finish' });
+  } else {
+    state = CompressorState.WAITING;
+  }
+};
diff --git a/tests/zipper-test.html b/tests/zipper-test.html
new file mode 100644
index 0000000..12ac530
--- /dev/null
+++ b/tests/zipper-test.html
@@ -0,0 +1,15 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Tiny web inteface to test the Zipper.</title>
+    <script src="zipper-test.js" type="module"></script>
+  </head>
+  <body>
+    <div>
+      <input id="zip-tester" type="file" multiple>
+      <span id="zip-uploader-label">Select a bunch of files to zip</span>
+    </div>
+    <button id="save" style="display: none">Save</button>
+    <div id="result"></div>
+  </body>
+</html>
\ No newline at end of file
diff --git a/tests/zipper-test.js b/tests/zipper-test.js
new file mode 100644
index 0000000..2117602
--- /dev/null
+++ b/tests/zipper-test.js
@@ -0,0 +1,64 @@
+
+import { Zipper } from '../archive/compress.js';
+
+const result = document.querySelector('#result');
+const fileInputEl = document.querySelector('#zip-tester');
+const saveButtonEl = document.querySelector('#save');
+let byteArray = null;
+
+/**
+ * @typedef FileInfo An object that is sent to this worker to represent a file.
+ * @property {string} fileName The name of this file. TODO: Includes the path?
+ * @property {number} lastModTime The number of ms since the Unix epoch (1970-01-01 at midnight).
+ * @property {Uint8Array} fileData The bytes of the file.
+ */
+
+/**
+ * @returns {Promise<}
+ */
+async function getFiles(fileChangeEvt) {
+  result.innerHTML = `Starting to load files`;
+  const files = fileChangeEvt.target.files;
+  const fileInfos = [];
+  for (const file of files) {
+    fileInfos.push(await new Promise((resolve, reject) => {
+      const fr = new FileReader();
+      fr.onload = () => {
+        resolve({
+          fileName: file.name,
+          lastModTime: file.lastModified,
+          fileData: new Uint8Array(fr.result),
+        });
+      };
+      fr.readAsArrayBuffer(file);
+    }));
+  }
+
+  result.innerHTML = `Loaded files`;
+
+  const zipper = new Zipper({ pathToBitJS: '../' });
+  byteArray = await zipper.start(fileInfos, true);
+  result.innerHTML = `Zipping done`;
+  saveButtonEl.style.display = '';
+}
+
+async function saveFile(evt) {
+  /** @type {FileSystemFileHandle} */
+  const fileHandle = await window['showSaveFilePicker']({
+    types: [
+      {
+        accept: {
+          'application/zip': ['.zip', '.cbz'],
+        },
+      },
+    ],
+  });
+
+  /** @type {FileSystemWritableFileStream} */
+  const writableStream = await fileHandle.createWritable();
+  writableStream.write(byteArray);
+  writableStream.close();
+}
+
+fileInputEl.addEventListener('change', getFiles, false);
+saveButtonEl.addEventListener('click', saveFile, false);