The ITK Software Guide is divided into two books. This second book details the toolkit architecture that supports reading and writing of images to files, introduces the most commonly used filters found in ITK, discusses ITK's capabilities for performing image registration, reviews ITK's commonly used segmentation components, and describes ITK's statistics functionalities. This book is the companion to The ITK Software Guide Book 1: Introduction and Development Guidelines. 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.