This chapter focuses on the implications of gender for mental health. The first and largest section of the chapter is devoted to depression. The sex difference in depression is described and then biological and social theories for this sex difference are offered. Biological theories focus on genes and hormones, largely concluding that biological factors interact with psychosocial factors to predict depression. Social factors that have been implicated in the sex difference in depression include learned helplessness, coping, rumination, and vulnerability to stressful life events. Because the sex difference in depression begins in adolescence, factors related to adolescence in particular, such as pubertal hormones and changes in body image, are reviewed. I then review the research on how people adjust to chronic illness, because chronic illness is often associated with depression. The chapter concludes with a discussion of eating disorders and suicide. Although men commit suicide more than women, women attempt suicide more than men. There are methodological explanations for these differences. I examine the predictors of suicide and suicide attempts in women and men.