Industrial and organizational psychology (or I/O psychology) is the study of the behavior of people in the workplace. Industrial and organizational psychology attempts to apply psychological results and methods to aid workers and organizations. It is also known as occupational psychology (the most common name in the United Kingdom) and work psychology (the direct translation of the standard term in German, Arbeitpsychologie).

Industrial and organizational psychologists use psychological testing to measure the knowledge, skills, abilities, and other characteristics (KSAOs) of people for a variety of employment-related purposes, such as selection for hiring or promotion, training and development, or measuring employee satisfaction. Historically, the job analysis has been the traditional means by which the essential KSAOs associated with any particular position are identified.

It is a fairly diverse field incorporating aspects of fields such as clinical psychology, social psychology, and psychometrics as well as broader social studies such as organizational theory, law, and gender issues.