The aim of this chapter is to dissect the human spermatozoon into its different parts and summarizes the current knowledge on the structure and function of the different components. The spermatozoon is a sophisticated machine shaped to fertilize the egg and to participate in embryo development. The integrity of all the sperm components is necessary to accomplish the mysterious process of fertilization: the plasma membrane with its specific domains for oocyte-sperm interaction, the acrosome rich in enzymes for the penetration of the zona pellucida of the oocyte, the haploid nucleus with a characteristic shape and chromatin structure different from that of somatic cells, the mitochondria the “powerhouse” of the spermatozoon and the flagellum, the engine for the movement.