Respondent learning theory is one of the earliest conceptual frameworks used to attempt to understand human development and behavior change across the lifespan and has been used for that purpose within social work for over 70 years. This chapter outlines some of the general principles by which people learn via responding conditioning processes, illustrating these from examples drawn from everyday life, as well as laboratory-based experimental demonstrations. How respondent conditioning is involved in the etiology and maintenance of problematic behavioral conditions experienced by social work clients is also described, with examples drawn from relatively simple reflexive responses (e.g., phobic anxiety) to more complicated affective reactions (e.g., racism). Lastly, the actual applications of respondent learning theory in the development of empirically-supported treatments useful in social work practice are reviewed.