Squeak is a modern open-source development environment for the classic Smalltalk-80 programming language. This book, intended for both students and developers, will guide you gently through the language and tools by means of a series of examples and exercises. We are making this book available to you under the Creative Commons Attribution-ShareAlike 3.0 license. You can either download the PDF for free from SqueakByExample.org, or you can buy a softcover copy from lulu.com. (You can also pay for the PDF download from lulu.com, if you would like to make a contribution to this effort.) Additional material is available from the book's web page at SqueakByExample.org.