Erectile dysfunction is a common and complex disease that has biological, clinical, and sociological significance. Scientific research with cell cultures, organ baths, and animal models has significantly advanced our understanding of the physiology of penile erection and common pathways involved in erectile dysfunction. Such studies have paved the way for pharmacological intervention and the modern era of highly effective treatments for ED. Continued investment in basic science research offers the potential for new and effective therapies for ED in the future. ED is intimately related to chronic medical and psychological conditions and may have significant psychosocial effects; for these reasons, psychological and epidemiologic research on ED is also important to advance the field. This chapter reviews fundamental tenets in the conduct of research and explore the current status of research on erectile dysfunction at physiological, clinical, and epidemiological levels.