BACKGROUND: Care homes provide long term care for older people. Countries with standardised approaches to residents' assessment, care planning and review (known as minimum data sets (MDS)) use the aggregate data to guide resource allocation, monitor quality, and for research. Less is known about how an MDS affects how staff assess, provide and review residents' everyday care. The review aimed to develop a theory-driven understanding of how care home staff can effectively implement and use MDS to plan and deliver care for residents. METHODS: The realist review was organised according to RAMESES (Realist And Meta-narrative Evidence Synthesis: and Evolving Standards) guidelines. There were three overlapping stages: 1) defining the scope of the review and theory development on the use of minimum data set 2) testing and refining candidate programme theories through iterative literature searches and stakeholders' consultations as well as discussion among the research team; and 3) data synthesis from stages 1 and 2. The following databases were used MEDLINE via OVID, Embase, CINAHL (Cumulative Index to Nursing and Allied Health Literature), ASSIA [Applied Social Sciences Citation Index and Abstracts]) and sources of grey literature. RESULTS: Fifty-one papers informed the development of three key interlinked theoretical propositions: motivation (mandates and incentives for Minimum Data Set completion); frontline staff monitoring (when Minimum Data Set completion is built into the working practices of the care home); and embedded recording systems (Minimum Data Set recording system is integral to collecting residents' data). By valuing the contributions of staff and building on existing ways of working, the uptake and use of an MDS could enable all staff to learn with and from each other about what is important for residents' care CONCLUSIONS: Minimum Data Sets provides commissioners service providers and researchers with standardised information useful for commissioning planning and analysis. For it to be equally useful for care home staff it requires key activities that address the staff experiences of care, their work with others and the use of digital technology. REGISTRATION: PROSPERO registration number CRD42020171323.