This book is a complete treatise on Quick Response (QR) Code symbolse"the square barcodes that can be read by smart phones. Widely used in marketing, they also reveal a creative solution to interesting challenges in computer graphics. The book describes the theory behind QR Code symbols and details the processes of encoding and decoding information in a QR Code symbol. The book explains sophisticated error correction techniques that allow a symbol to be scanned even if it is partially obscured, and it delves into the theoretical foundation of error correcting codes using basic mathematics. Java source code for constructing, scanning, and decoding QR symbols will be available for download.