My research is directed toward developing human-like software agents for virtual training environments and to use these computational methods to concretize psychological theories of human behavior. Specifically, I investigate how algorithms can control the behavior of characters in virtual worlds, endowing them with an ability to think and engage in socio-emotional interactions with human users, using both verbal and nonverbal communication. Such methods can deepen our understanding of human behavior, by instantiating and systematically manipulating psychological theories. They also have wide application to such areas as training, entertainment and clinical diagnosis, assessment and treatment.