Recognizing the import of the problem, the U.S. Department of Justice has established a Violence Against Women Office, and many States have enacted legislation to protect victims and deal with perpetrators. The dynamics of relationship aggression need to be understood so that effective interventions and prevention programs can be developed. The current status of research on relationship aggression is reviewed. Several omissions in the research are noted, such as ignorance of the potential contribution of biological factors. Recent research regarding the relevance of biological factors is examined, with emphasis on theories of human behavior that incorporate biological influences, the serotonin hypothesis (a neurotransmitter implicated in many psychiatric and psychological conditions and in the etiology of aggressive behavior), and the effect of head injury on relationship aggression. A biopsychosocial model is described to explain relationship aggression, and suggestions for future research are offered. 79 references and 1 figure