Maintenance and generalization have been inconsistently defined in the behavior analytic literature. The term "treatment relapse" is used commonly in the medical and mental health literature to refer to the return of a condition that was previously considered successfully treated. Basic behavioral researchers have studied relapse related to behavioral momentum theory (BMT). The present authors discuss the differences in terminology and propose the field adopt the term "treatment relapse" when treatments are no longer effective or when their effects are not present in settings in which the treatment was not originally implemented. The implications BMT has for designing behavioral interventions to minimize or avoid treatment relapse are discussed along with a brief review of applied studies that demonstrate BMT may be useful for practitioners and applied researchers.