"Psychologische Typen" by C. G. Jung is a book published in 1921. Jung introduces a groundbreaking framework for understanding human personality through four functions of consciousness—Sensation, Intuition, Thinking, and Feeling—shaped by two attitudes: extraversion and introversion. This creates eight distinct psychological types, each revealing tensions between conscious and unconscious aspects of personality. Born from Jung's attempt to reconcile competing theories of Freud and Adler, this work became the foundation for modern personality typology systems, fundamentally changing how we understand human differences.