The concept of treatment fidelity (integrity) is important across a diversity of fields that are involved with providing treatments or interventions to individuals. In medicine, the concept of treatment compliance or treatment adherence is an important and problematic issue. In the field of nutrition, the concept of dietary adherence is important for successful outcomes. In the fields of rehabilitation and substance abuse, the term program implementation captures the concept of treatment fidelity. Finally, in the field of applied behavior analysis, the concept of procedural reliability is commonly used to refer to treatment fidelity. Despite variations in terminology across these diverse fields, the concern that treatments or interventions are delivered as prescribed or intended is of paramount importance to document that changes in individuals’ functioning (medical, nutritional, psychological, or behavioral) are due to treatments and not from uncontrolled, extraneous variables.