Experiential acceptance, which involves "having," or "allowing" private experiences, has recently gained much attention in the cognitive-behavioral literature. Acceptance, however, may be considered a common factor among psychotherapeutic traditions. The purposes of this paper are to examine the historical roots of acceptance and to discuss the forms of and theoretical rationales for which the concept of acceptance has been recently introduced into the cognitive-behavioral literature, with an emphasis on acceptance and commitment therapy (ACT; Hayes, Strosahl, & Wilson, 1999). It is hoped that clarification of the theoretical basis underlying acceptance-based approaches, as well as a comparison of various forms of psychotherapy with regard to their emphasis on acceptance, will promote heightened understanding and stimulate more rigorous exploration of treatment efficacy.