Most psychological disorders and problem behaviors are characterized by very high rates of postremittance relapse. Thus, advances in the long-term efficacy of psychological interventions require understanding the causes and processes of relapse, with the ultimate goal of developing strategies that reduce the probability of relapse. Existing psychological theory and interventions relevant to relapse and relapse prevention (RP) are reviewed, with a focus on addictive behaviors. The past two decades have produced increased attention toward the relapse problem and important advances in the conceptualization of relapse (i.e., as a process rather than a discrete event). Further progress will require the translation of basic theory into applied theory, the development of integrative theories of relapse, and the design and testing of theory-based, multimodal RP interventions.