This chapter is a nascent effort to describe the zeitgeist or social‐historical context of industrial‐organizational psychology by identifying various dynamic influences that shaped the rise of the discipline during the past 100 years in the United States. Significant developments and persons were examined within the overall social, cultural and political contexts of the times to answer the question, “
Why
were psychologists studying behavior in work settings and applying psychology to improve the workplace?” The first section encapsulates I‐O psychology's growth: industrial‐organizational psychology shifted from a simple, narrowly defined technical field focused on individual issues for accomplishing organizational objectives to a complex, broad scientific and applied discipline emphasizing individual and organizational issues for achieving both individual and organizational goals. The second section describes the dynamic forces that shaped I‐O psychology and reveals that the discipline's evolution was the result of confluences of several external (socioeconomic, business, legal, military, technology, psychology) and internal forces (individuals, theories, and applications). These forces, along with other influences (e.g., interdisciplinary fields), interacted in shaping both the science and practice of industrial‐organizational psychology. The history presented in this chapter is not intended to be a comprehensive description of industrial‐organizational psychology content or a duplication of historical accounts previously written.