Psychological Types, first published in 1921, stands as one of Carl Gustav Jung's most influential and enduring works. In this groundbreaking volume, Jung introduces the foundational concepts of introversion and extraversion, alongside his theory of four psychological functions—thinking, feeling, sensation, and intuition. These ideas form the basis of Jung's typology, which has since influenced countless fields, from psychology and education to business and personality testing. In this richly layered text, Jung explores the historical and philosophical roots of psychological orientation, referencing figures such as Goethe, Nietzsche, and Schiller to illustrate how psychological types manifest across cultures and intellectual traditions. He proposes that people differ in how they perceive the world and make decisions—distinctions that go beyond mere behavior to reflect deep-seated orientations of consciousness. The book also addresses the tension between rational and irrational attitudes and explains how individuals gravitate toward dominant psychological functions while often neglecting others. These imbalances, Jung argues, can lead to psychological conflict, which may be resolved through the process of individuation—a central idea in Jungian thought. This translation by H. G. Baynes, a close collaborator of Jung, maintains the intellectual rigor and clarity of the original German text, making the complex theories accessible to an English-speaking audience.