This article reviews 100 years of research on individual differences and their measurement, with a focus on research published in the Journal of Applied Psychology. We focus on three major individual differences domains: (1) knowledge, skill, and ability, including both the cognitive and physical domain; (2) personality, including integrity, emotional intelligence, stable motivational attributes (e.g., achievement motivation, core self-evaluations), and creativity; and (3) vocational interests. For each domain, we describe the evolution of the domain across the years and highlight major empirical, theoretical, and methodological developments, including relationships between individual differences and job performance, job satisfaction, career development, and other aspects of organizational behavior. We conclude by discussing future directions for individual differences research.