The estimated prevalence of erectile dysfunction (ED) ranges from 15 - 50 million men in the United States alone, with all age groups of men affected. Despite still-existing taboos surrounding male impotence, more men are seeking help and treatment with the advent of newer treatment options in recent years, most notably oral PDE-5 inhibitors that shed light on the primary vascular cause and treatment target in most cases. In the majority of men, ED has a physical cause and can be effectively treated. Increased knowledge of cause and treatment options, however, requires clinicians to become acquainted with side effects of drugs, alternative treatments, new research in the field, and potential disease conditions that might co-exist with ED. Part of the Oxford American Urology Library, this practical manual illuminates the pathophysiology of erectile dysfunction and approaches to diagnostic evaluation and therapeutic options, including specifics of ED in men with chronic diseases such as diabetes, hypertension, coronary artery disease, heart failure, and chronic kidney disease. All currently available treatment options from prostaglandins to vacuum devices, PDE-5 inhibitors, and interventional and surgical therapies are described for their efficacy and safety based on the published literature and ongoing research trials.