This book is about IT architecture set against the background of the practical insights gained at HP (Hewlett-Packard) since 1986 and formalized in the HP methodology for IT Strategy and Architecture (ITSA). The important message is that architecture is used to solve problems or exploit opportunities and is not used for the sake of architecture. Core to this is the concept of a seamless chain of justification that unites stakeholders in defining, reinforcing, and supporting the single best fitting IT business solution. This book teaches the IT architecture practitioner how to align the different views and interests of these stakeholders into coherent IT architecture artifacts by permeating the business, functional, technical, and implementation perspectives.