BackgroundHealth-care systems are increasingly moving towards more integrated approaches. Shared decision-making (SDM) is central to these models but may be complicated by the need to negotiate and communicate decisions between multiple providers, as well as patients and their family carers; this is particularly the case for older people with complex needs.ObjectivesTo provide a context-relevant understanding of how models to facilitate SDM might work for older people with multiple health and care needs and how they might be applied to integrated care models.DesignRealist synthesis following Realist and Meta-narrative Evidence Syntheses: Evolving Standards (RAMESES) publication standards.ParticipantsTwenty-four stakeholders took part in interviews.Data sourcesElectronic databases including MEDLINE (via PubMed), The Cochrane Library, Scopus, Google and Google Scholar (Google Inc., Mountain View, CA, USA). Lateral searches were also carried out. All types of evidence were included.Review methodsIterative stakeholder-driven, three-stage approach, involving (1) scoping of the literature and stakeholder interviews (n = 13) to develop initial programme theory/ies, (2) systematic searches for evidence to test and develop the theories and (3) validation of programme theory/ies with stakeholders (n = 11).ResultsWe included 88 papers, of which 29 focused on older people or people with complex needs. We identified four theories (context–mechanism–outcome configurations) that together provide an account of what needs to be in place for SDM to work for older people with complex needs: understanding and assessing patient and carer values and capacity to access and use care; organising systems to support and prioritise SDM; supporting and preparing patients and family carers to engage in SDM; and a person-centred culture of which SDM is a part. Programmes likely to be successful in promoting SDM are those that create trust between those involved, allow service users to feel that they are respected and understood, and engender confidence to engage in SDM.LimitationsThere is a lack of evidence on interventions to promote SDM in older people with complex needs or on interprofessional approaches to SDM.ConclusionsModels of SDM for older people with complex health and care needs should be conceptualised as a series of conversations that patients, and their family carers, may have with a variety of different health and care professionals. To embed SDM in practice requires a shift from a biomedical focus to a more person-centred ethos. Service providers are likely to need support, both in terms of the way services are organised and delivered and in terms of their own continuing professional development. Older people with complex needs may need support to engage in SDM. How this support is best provided needs further exploration, although face-to-face interactions and ongoing patient–professional relationships are key.Future workThere is a need for further work to establish how organisational structures can be better aligned to meet the requirements of older people with complex needs. This includes a need to define and evaluate the contribution that different members of health and care teams can make to SDM for older people with complex health and care needs.Study registrationThis study is registered as PROSPERO CRD42016039013.FundingThe National Institute for Health Research Health Services and Delivery Research programme.