It is illegal to own a pet monkey in most states, so outside of zoos, animal sanctuaries, and places where regulated medical research can take place, you **cannot legally buy a pet monkey**. However, it is possible to adopt one, and some primates, such as marmosets, may be available for purchase from breeders.
Animal sanctuaries may also allow for primates to be adopted. If you do decide to adopt a monkey, you must be prepared for their special needs and the fact that they can live up to 40 years.