This book includes a comprehensive investigation of the concept of meaning, focusing on its structure, function, and materials. In terms of structure, it is proposed that meaning is a unit which consists of two components: the carrier of meaning, called referent, to which meaning is assigned, and the meaning assigned to the referent, called meaning value. In terms of function, meaning is designed to identify inputs from outside and inside the organism, so as to enable responding to them in forms adequate for the psychological system. Otherwise expressed, meaning turns stimuli into potential triggers of reactions on all psychological levels. In terms of materials, meaning consists of cognitions, which are neither expected to be logical or rational nor are necessarily subjected to awareness, voluntary control or verbal expression. So, in practice, meaning consists of cognitive units, which are characterized in terms of referents and meaning values, forming sequences and networks, providing identification of stimuli and potentialities for grasping reality, reacting to it and transforming it. This book is a culmination of the author's decades of academic experience in pursuit of an understanding of meaning. In this book's thirteen chapters, meaning is explored through a variety of perspectives, including those drawn from evolutionary psychology, linguistics, cognition, personality, and other fields. Also, exercises are included that provide tasks designed to allow readers to familiarize themselves with the system of meaning elucidated in the book.