The goal of this book is to explain the many methods of rendering a digital image in a computer and what is ray tracing. Ray tracing is one part of the continuum of rendering solutions on the path to a perfect photorealistic image. Ray tracing has several cousins with a similar name such as Path Tracing and ray casting, which sometimes get used interchangeably; that is not correct and can be confusing. One of the objectives of this book is to establish clear delineation between those other technologies whose only common element is a word, but not the technology, algorithm, or result. Ray tracing holds the promise of providing us with the most cost-effective photorealistic images possible. The process has been criticized for being such an enormous consumer of computer resources, but new developments in hardware and algorithms are changing that and making real-time ray tracing not only possible but practical.