Acceptance is integral to several cutting-edge behavior therapies. However, several questions about acceptance remain to be clearly answered. First, what does acceptance look like, and can it be observed and measured? Second, what are the behavioral principles involved in the promotion of acceptance? Third, when is acceptance indicated or contraindicated as a therapeutic goal? The current paper attempts to clarify answers to these questions. The goal is to provide a conceptualization of the what, how, and when of acceptance that is accessible to behavior analysts, both to promote our understanding of acceptance as a behavioral phenomenon and to facilitate its empirical study and therapeutic utility.