This book serves as an introduction to computer science at the undergraduate level. It provides a detailed overview of the state-of-the-art concepts in human computer interaction (HCI). The main topics in this book is focusing on cognitive sciences, where the basic principles and factors of human computer interaction were discussed in relation to contributions from other fields such as social and organizational psychology. Furthermore, the mental, physical and social aspects of human information processing were also described. Technologies of human computer interaction that has to do with input devices such as keyboard, touchpad, etc., and output devices such as visual display unit (VDU), printer and plotter were also dealt with in details. Similarly, technologies in interactions such as virtual reality and windowing systems were explained in this book. Finally, topics related to interface design evaluations, prototypes, and user requirements analysis were also considered in line with relevant figures, illustrations, and exercises, to enable readers understand the concepts of these topics. In summary, human computer interaction is not only limited to computer science but other fields of human endeavour such as human psychology and health sciences. Consequently, this book is expected to serve as a reference in relevant topics within the area of human computer interaction, both at the undergraduate and postgraduate levels.