This book focuses on the current basic science research of hypospadias and genital development. Congenital anomalies of the genitalia are the second most common birth abnormality besides congenital heart defects. Genital anomalies come in many varieties with the most common abnormality being hypospadias. The etiology of hypospadias remains unknown and the incidence is doubling in western countries with no definable explanation. It therefore seems especially germane to study this common congenital anomaly with a baseline incidence of 1/125-250 newborn males.