Nonhuman primates constitute one of the most diverse mammalian orders and are of particular importance in biomedical research due to their close anatomical, physiological and genetic resemblance to humans. This phylogenetic proximity enables studies in nonhuman primates to yield critical insights into the organisation and function of the human body and mind. Among them, macaques and marmosets are the most widely used species, each offering distinct advantages for experimental and translational research. This chapter introduces key aspects of nonhuman primates’ biology, includeing an overview of their anatomy, genetics and locomotor adaptations, as well as their feeding strategies, social behaviour and abnormal behaviours. It concludes with a brief overview of infectious diseases and zoonoses, which pose particular risks in laboratory environments where close human–primate contact occurs.