This research paper delves into the origins and development of differential psychology, exploring its foundational principles and significant contributions to the field of psychological science. It traces the historical context from which differential psychology emerged, examining the pioneering work of key figures and the evolution of methodologies used to assess individual differences. The study also investigates the core concepts within differential psychology, such as intelligence, personality, and their interrelationships, providing an overview of how these concepts shaped the modern understanding of human behavior. Furthermore, the paper analyzes the influence of differential psychology and its ongoing relevance in contemporary psychology.