Ignorance is a popular explanation for dysfunctional behavior. This perspective on human dysfunction has given rise to a family of behavior-change strategies that target ignorance. This chapter begins with an overview of the facts and assumptions about human psychology that have guided the development of the approach to behavior change and then proceeds to an examination of the strategies themselves and their effectiveness. If ignorance is what stands in the way of people exhibiting desirable behavior, then the most obvious strategy for changing behavior is to alleviate their ignorance—help them to know better so they will behave better. One behavioral domain in which social norms marketing has proven highly effective is household energy consumption. Ignorance is neither a complete nor an adequate explanation for dysfunctional behavior, however, for it ignores the critical role that values play in shaping behavioral choices.