Resident-to-resident aggression (RRA) between long-term care residents includes negative and aggressive physical, sexual, or verbal interactions that in a community setting would likely be construed as unwelcome and have high potential to cause physical or psychological distress in the recipient. Although this problem potentially has high incidence and prevalence and serious consequences for aggressors and victims, it has received little direct attention from researchers to date. This article reviews the limited available literature on this topic as well as relevant research from related areas including: resident violence toward nursing home staff, aggressive behaviors by elderly persons, and community elder abuse. We present hypothesized risk factors for aggressor, victim, and nursing home environment, including issues surrounding cognitive impairment. We discuss methodological challenges to studying RRA and offer suggestions for future research. Finally, we describe the importance of designing effective interventions, despite the lack currently available, and suggest potential areas of future research.