Tremendous advances in the genetic underpinnings of obesity have emerged in recent years. Curiously, behavioral genetic methods have provided relatively less information on the environmental influences and intermediary behaviors which promote human obesity. This situation in unfortunate since human obesity is, in part, environmentally determined and the result of behaviors such as eating and physical (in)activity. This article has several goals. First, it outlines reasons why behavior qua behavior should be a specific focus of obesity-oriented behavioral genetic designs. Second, possible explanations for why behavior has been underinvestigated are explored. Third, data regarding the genetic/ environmental architecture of various obesity-related phenotypes (e.g., food intake, physical activity, etc.) are reviewed. Fourth, a commentary on the importance of gene-environment interactions is offered. Finally, suggestions for future research, including a list of possible "candidate environments" and "candidate intermediary behaviors," are offered.