This chapter explores how the relationship between obesity and depression is complex; it differs by age, gender, socioeconomic status, race, degree of obesity, and nation. It describes all three of these lines of argument: obesity as a contributor to depression, depression as a contributor to obesity, and depression and obesity as mutually reinforcing conditions. The chapter briefly summarizes broad patterns evident in associations between depression and obesity. Depression during childhood and adolescence is linked with higher body mass index and elevated risk of obesity by early to mid-adulthood. It is shown that one way in which obesity may act on depression is by increasing the likelihood that individuals will be dissatisfied with their appearance. It is today clear that obesity and depression are linked, though to what degree and through what mechanisms remains the topic of much inquiry.