Technical Abstract: Toxoplasma gondii is a protozoan parasite of warm-blooded animals including humans. It has a worldwide distribution. Cats, including all felines, are its definitive hosts and excrete environmentally-resistant oocysts in their feces. Hosts become infected by ingesting food or drink contaminated with oocysts or by ingesting undercooked meat infected with T. gondii. It causes mental retardation and loss of vision in congenitally-infected children and abortion in livestock. This chapter describes life cycle, epidemiology, diagnosis, and prevention of T. gondii in humans and animals.