This chapter presents some closing thoughts on the key concepts discussed in the preceding chapters of this book. The book focuses on detailed descriptions of applied behavioral techniques and the power of such techniques to change behavior, rather than describing studies on topics of social interest. It extends the account of behavior analysis provided earlier in several ways. Applications to health and are reviewed, both because of their inherent importance, and because they illustrate that the techniques shown to be effective in earlier chapters can be applied more widely. To illustrate the potential of applied behavior analysis to embrace a broad field, the book focus on a select number of topics of wide social concern in which behavioral principles have been systematically applied and researched. It introduces the concept of social validity, and operationalizes social validity and demonstrates the potential benefits of collaboration to both the researcher and the community.