This book is intended to give an overview of important issues concerning Human-Computer Interaction and information visualization. It is based on an IFIP [4] workshop that took place during the Interact’09 conference in Uppsala [3]. This workshop, co-organized by IFIP WG TC13.7 on “HCI and Visualization” [2] and the European VisMaster Coordinated Action [5], surveyed and expanded our understanding of the cognitive and perceptual issues of interactive visualization and visual analytics and brought together researchers interested in these issues. It outlined the research required to understand what aspects of analysis match human capabilities most closely, and how interactive visual support should be designed and adapted to make optimal use of human capabilities in terms of information perception and processing.