A timely contribution to the literature of human-computer interaction, this text explains how to build interactive software applying principles from the fields of human-computer interaction, psychology, and software engineering. The book's primary emphasis is on how to build interactive software, with a secondary emphasis on what makes systems easy to use. It uses several different styles of user interfaces (desktop, mobile, web) to illustrate the principles behind building interactive software, and employs several languages and technologies throughout. The coverage includes new technologies, such as mashups and RSS feeds, and a discussion of social software principles.