This chapter explains the role of gametogenesis in human reproduction and development, and describes the process of spermatogenesis, including the role of spermiogenesis. The formation of gametes is gametogenesis and comes in two varieties: spermatogenesis in men and oogenesis in women. The spermatozoon is a differentiated cell that is destined to fertilize an egg or die. The chapter presents the structure of the sperm and how this structure assists in its function—fertilizing the egg and the process of oogenesis. It explores the structure of the egg and how this is suited to its role of being fertilized and giving rise to the embryo. During development, the germ cells arise outside the embryonic body and subsequently migrate into the developing gonads. The chapter discusses the similarities and differences between the male and female gametes, including lifespans, replenishment, relative number of gametes, and structure. Human males can produce gametes from puberty into advanced old age because the testes contain stem cell populations.