Spermatozoa are produced in the testicles. The testicles are part of the male reproductive system and are responsible for producing and storing sperm. Sperm are the male reproductive cells that are necessary for fertilization, which is the process by which sperm combine with an egg to form an embryo. The testicles are located outside the body in a sac called the scrotum. This location helps to maintain a temperature that is cooler than the body, which is necessary for optimal sperm production. The production of sperm is a continuous process that starts during puberty and continues throughout a man's life.