To synthesize aged care provider, resident and residents' family members' perspectives and experiences of medication administration in aged care facilities; to determine the incidence of medication administration errors, and the impact of medication administration on quality of care and resident-centredness in aged care facilities. A mixed-methods systematic review. CRD42023426990. The AMED, CINAHL, MEDLINE, EMBASE, EMCARE, PsycINFO, Scopus and Web of Science core collection databases were searched in June 2023. Included studies were independently screened, selected and appraised by two researchers. The Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) checklist was followed, with the Mixed Methods Appraisal Tool was used for critical appraisal. Convergent synthesis of data, thematic synthesis and meta-analysis were performed. One hundred and twenty-eight studies were included (33 qualitative, 85 quantitative and 10 mixed-methods). Five themes were formulated, including 1) Staffing concerns, 2) The uncertain role of residents, 3) Medication-related decision-making, 4) Use of electronic medication administration records and 5) Medication administration errors. Educational interventions for aged care workers significantly reduced medication administration errors, examined across five studies (OR = 0.37, 95%CI 0.28-0.50, p < .001). Medication administration in aged care facilities is challenging and complex on clinical and interpersonal levels. Clinical processes, medication errors and safety remain focal points for practice. However, more active consideration of residents' autonomy and input by aged care workers and providers is needed to address medication administration's interpersonal and psychosocial aspects. New directions for future research should examine the decision-making behind dose form modification, aged care workers' definitions of medication omission and practical methods to support residents' and their family members' engagement during medication administration. It is important that medication administration in aged care facilities be more clearly acknowledged as both a clinical and interpersonal task. More attention is warranted regarding aged care workers clinical decision-making, particularly concerning dose form modification, covert administration and medication omissions. Resident-centred care approaches that support resident and family engagement around medication administration may improve adherence, satisfaction and quality of care. What Problem Did the Study Address? Medication administration in aged care facilities is a complex clinical and interpersonal activity. Still, to date, no attempts have been made to synthesize qualitative and quantitative evidence around this practice. There is a need to establish what evidence exists around the perspectives and experiences of aged care workers, residents and resident's family members to understand the challenges, interpersonal opportunities and risks during medication administration. What Were the Main Findings? There is a lack of empirical evidence around resident-centred care approaches to medication administration, and how residents and their families could be enabled to have more input. Dose form modification occurred overtly and covertly as part of medication administration, not just as a method for older adults with swallowing difficulties, but to enforce adherence with prescribed medications. Medication administration errors typically included medication omission as a category of error, despite some omissions stemming from a clear rationale for medication omission and resident input. WHERE AND ON WHOM WILL THE RESEARCH HAVE AN IMPACT?: The findings of this systematic review contribute to aged care policy and practice regarding medication administration and engagement with older adults. This review presents findings that provide a starting point for aged care workers in regards to professional development and reflection on practice, particularly around clinical decision-making on dose form modification, medication administration errors and the tension on enabling resident input into medication administration. For researchers, this review highlights the need to develop resident-centred care approaches and interventions, and to assess whether these can positively impact medication administration, resident engagement, adherence with prescribed medications and quality of care. This systematic review was reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (Page etal., 2021). No patient or public contribution to this systematic review.