Acceptance and commitment therapy (ACT; Hayes, Strosahl, & Wilson, 1999) has been identified as a modern behavior therapy and has a substantive body of supporting evidence that includes over 200 randomized controlled trials. ACT has been linked directly to relational frame theory (RFT; Hayes, Barnes-Holmes, & Roche, 2001)-a behavior-analytic account of human language and cognition that relies on the concept of derived stimulus relations. RFT also has a growing body of empirical evidence (Barnes-Holmes, Finn, McEnteggart, & Barnes-Holmes, in press; O'Connor, Farrell, Munnelly, & McHugh, 2017). The basic idea behind both RFT and ACT is that the evolution of human language, conceptualized as derived relational responding, creates a type of psychological suffering that is largely unique to humans. RFT constitutes the basic theory behind this assertion, and ACT, as a clinical intervention, is designed to deal with the psychological problems that human language creates for our species (Törneke, 2010; Villatte, Villatte, & Hayes, 2015). This article provides a tutorial on the links between ACT and derived stimulus relations, particularly through the lens of RFT. Although RFT is sometimes seen as providing the basic behavioral science underpinning ACT, it is perhaps more accurate to say that they have co-evolved. Thus, RFT did not give rise directly to ACT, and ACT did not backward engineer RFT, but the two are interrelated. This tutorial thus aims to articulate the clear links between the theory and the application (where they exist) and how RFT suggests functional-analytic ways in which clinically relevant behavior can be understood and manipulated. This article will first describe the conceptual