The state-of-the-art treatment of challenging behaviors is discussed in terms of methodological and conceptual advances in applied behavior analysis. A protocol for addressing these behaviors is presented that includes a functional analysis, preference assessment, empirically validated treatment with assessments of both inter-observer agreement and procedural integrity, and assessment of outcome generality and maintenance. Key words: Challenging behaviors, preference assessment, functional analysis, establishing operations, behavioral momentum ********** Challenging behaviors are challenging because they are highly resistant to change. In addition, they are often harmful to the people who exhibit them or to others, a factor that substantially increases clinical concern. In the past decade, applied behavior analysts have become increasingly well-equipped to respond to challenging behaviors. Refined methodologies such as functional analyses and preferences assessments now help them to empirically determine variables maintaining the problem behaviors and to identify effective reinforcers for individuals who need treatment. With this information in hand, applied behavior analysts can develop treatment procedures that are more likely to be effective than they might be able to do otherwise. Additional refinements in principles including the differentiation between establishing operations and discriminative stimuli (Michael, 1982), and the exploration of applied use of concepts such as behavioral momentum (Nevin, 1996) have broadened the assessment and intervention procedures available to treat clinical problems. From the applied behavioral research, a protocol emerges for addressing challenging behaviors that captures the new developments in the field. It includes, with some variation, (a) a functional analysis, (b) a preference assessment, (c) a treatment plan based on the functional analysis, (d) an empirically validated treatment implementation with assessments of both inter-observer agreement and procedural integrity, and (e) an assessment of outcome generality and maintenance. FUNCTIONAL ANALYSIS It is easy to assume that all behavioral interventions are based on an examination of the contingencies related to the behaviors of concern. This, however, is not always the case. Quite often applied behavior analysts simply control behaviors by employing powerful reinforcers or punishers that override the existing maintaining relationships. Such an approach can be problematic because it increases the likelihood that any behavior changes realized might not be sustained once the consequences are removed. The powerful contingency may only suppress, but not weaken, the maintaining relationships. As a result, once the potent reinforcer or punisher is no longer provided, the discriminative stimuli that previously occasioned the behavior may resume their function, which allows former consequences to re-establish control. If this occurs, it necessitates development of procedures to ensure maintenance of treatment gains, or indefinite implementation of treatment. When a functional analysis is included in the standard treatment protocol for addressing challenging behaviors, it directs the applied behavior analyst's attention away from treatments involving powerful consequences to those that change how the challenging behavior functions for the individual who exhibits it. By observing and collecting data on the relationship between antecedent events, behaviors, and consequences, the applied behavior analysts learns how the environment is maintaining the behavior in question. Treatment, then, involves changing the relationship of those contingencies and making them no longer effective. Iwata and colleagues advance functional analysis procedures that typically call for a multi-element analysis in which several contingencies are evaluated in succession. These contingencies usually represent negative, positive, and automatic reinforcement; however, establishing operations and other antecedent events may also be manipulated. …