OBJECTIVES: Resident-to-resident elder mistreatment (R-REM) between residents living in residential aged care (RAC) services is a challenging issue in relation to the care of older people. Evidence suggests that R-REM, such as verbal, physical, and sexual conflict between residents, is a common and pervasive issue. This review examines the frequency with which R-REM occurs in RAC services; identifies the types of R-REM that occur; and provides an overview of the reported characteristics of both the victim and perpetrator involved in the R-REM event. DESIGN: A systematic review was conducted. We searched MEDLINE, EMBASE, CINAHL, PsycINFO, Ageline, and Cochrane Library to identify qualitative and quantitative studies published in the English language. SETTING AND PARTICIPANTS: Residents living in RAC services. MEASURES: Data on frequency and characteristics were collated, and aggregate proportions were calculated where possible. RESULTS: Twenty-six studies were identified; most (n = 20) were published in the United States. The overall proportion of residents engaged in R-REM was provided by 7 quantitative studies with the estimated frequency reported to be 12% to 23%. For qualitative studies, the number of care staff reporting to have observed R-REM ranged from 18.7% to 98.0%. Physical and verbal abuse were the most commonly reported types of mistreatment. Characteristics of the perpetrator of R-REM were reported in 12 (46.2%) studies. Overall, the mean age of perpetrators was 80.93 years, most were men (83.2%), and 64.4% had dementia and/or Alzheimer diagnosis. Characteristics of the victim and the history of R-REM were largely omitted from the published studies. CONCLUSION AND IMPLICATIONS: The findings from the review broaden understanding on the extent of R-REM; the individual and event characteristics and ultimately support care planning, policy, and direction for future research. To improve understanding, quality of care, and RAC residents' well-being, further studies are recommended to address the identified gaps in knowledge.