The success of behavior-analytic interventions depends on well-designed procedures and their accurate, consistent implementation. This chapter explores the critical role of implementers, the challenges they face, and strategies to support them. Drawing parallels to adherence research in medicine, this chapter examines factors influencing adherence (consistency of implementation) and fidelity (accuracy of implementation) to behavior-analytic interventions, including training, contingencies, and the implementer–specialist relationship. Additionally, the authors discuss how developing other implementer repertoires, such as psychological flexibility and problem-solving, can enhance adherence and fidelity. Finally, the authors recommend embedding planning for adherence and fidelity within an evidence-based practice framework to optimize intervention outcomes.