The understanding of the pathophysiology of erectile dysfunction (ED) has advanced significantly over the past two decades. In this ebook, we provide an in-depth analysis of the current knowledge of the pathophysiology of ED in order to provide the reader with an up-to-date and comprehensive understanding of the pathophysiology of ED, which is complex but fascinating. Intensive and intricate mechanisms govern the development of ED. These mechanisms involve complex interaction between vascular, hormonal and neural regulation. Current research on the central regulation of ED is key for the advancement of our understanding of this complex disease. Recent advances in our knowledge of the vascular mechanisms regulating penile erection led to appreciation of ED as an early symptom of cardiovascular disease. Major health concerns such as atherosclerosis, hyperlipidemia, hypertension and diabetes have become well integrated into the investigation of ED. Extensive research on the mechanisms involved in the regulation of penile erection have led to unparalleled advances in the understanding of general vascular regulation. However, many unknowns remain, which provides vast opportunities for future basic and clinical investigations.