The ITK Software Guide is divided into two books. This first book provides a general introduction to ITK including instructions for building and installing ITK; introduces the general architecture and design as well as basic system concepts; and explains how to create your own classes, extend the system, and be an active participant in the open-source ITK community. This book is the companion to The ITK Software Guide Book 2: Design and Functionality. ITK is an open-source, cross-platform software toolkit that provides an extensive suite of tools for image analysis. For over a decade, researchers and developers around the world have processed their MRI, CT, ultrasound, PET, fluoroscopy, and microscopy data with ITK. Developed through extreme programming methodologies, ITK employs leading-edge algorithms for registering and segmenting multidimensional data.