The understanding of embryology provides a foundation for the mastery of anatomy. In the treatment of men with infertility, it is only appropriate that one deals with the basics of fetal development of the male reproductive tract. This chapter reviews the germ layers from which all tissues organize themselves and develop, and also reviews the ductal system and its critical role in reproduction. The cloaca, as incorporated yolk sac, is an endoderm-lined cavity, anchored at the caudal end by the cloacal membrane. The mesonephric ducts, which are mesodermal structures, are connected to the urogenital sinus bilaterally. The common excretory ducts eventually move into the prostatic part of the urethra and become known as the verumontanum. Testosterone stimulates numerous changes in the existing ductal system. In the presence of testosterone, the phallus lengthens and enlarges to form the penis.