Normal sexual function is a biopsychosocial process; sexual dysfunction almost always has organic and psychologic components, and it requires multidisciplinary, goal-directed evaluation and treatment. Factors such as aging, declining testosterone levels, medical illness, certain medications, and comorbid depressive illness can contribute to sexual dysfunction. Erectile dysfunction (ED) is the most common male sexual dysfunction encountered in the clinical setting. Comorbidity between ED and depressive illness is high, but the causal relationship is unclear, and likely bidirectional. In this article, we review the existing literature on the relationship between depression and ED.