Many behavioral researchers and clinicians hold the view that behavioral assessment and therapy are part of a science that is based on reliable and observed behavior. However, they forget that even in behavioral therapy, case formulation is an art that is ultimately based on the therapist's hypotheses and judgments about the problem behaviors, causal variables, and functional relations among multiple behaviors, environments, and so on. Moreover, as Haynes and O'Brien point out, case formulation affects clinical intervention, and many uncontrolled factors moderate treatment effects. These moderator variables include the person's goals and strengths, presence of medical and psychiatric problems, characteristics of the treatment environment, use of recreational and prescribed drugs, social support, and others. To their credit, the authors present a clinically astute model that relates behavioral assessment to good case formulation, which leads to appropriate clinical intervention that will result in enhanced treatment outcomes.