This book is the first part of an introduction to the field of cognitive psychology and the basic cognitive processes. Specifically, it covers in depth the cognitive functions of attention, perception, and memory. It also includes a broad overview of the history of cognitive psychology and its methods, while discussing the topics of the physiology of cognitive processes and the organization and representation of knowledge. It is primarily written for undergraduate psychology students, but at the same time it serves as a modern and user-friendly handbook for the reader who, without any previous contact with the science of psychology, wants to study the processes that allow us to understand the world.