Background <p>Healthcare spending in high-income countries has outpaced economic growth in recent decades, with hospital services accounting for a high proportion of it. Health systems in most high-income countries have explored models of intermediate care to provide less resource-intensive care outside hospitals. Different models of admission avoidance intermediate care have been introduced in countries with varying approach, capacity and settings e.g. hospital-at-home (HaH), inpatient admission avoidance intermediate care (AAIC) schemes. Although approaches like HaH have shown to be effective in providing care at a lower cost, inpatient AAIC schemes are less studied.</p> Materials and methods <p>We conducted a realist review to capture evidence for explaining effectiveness in regards to utilisation and quality of care provided, and cost of admission avoidance intermediate care services. We searched for literature in three online databases (Ovid Medline, Embase and CINAHL) plus supplementary search methods (forward and backward citation searching) during October-December 2022 followed by a supplementary search in January 2026 to: (1) formulate initial programme theories and (2) refine programme theories. A total of 2625 studies from database search and eight more from manual searches were retrieved. After screening, full text of thirty five papers were explored out of which = analysis of eleven qualitative papers was included in the review for the formulation of programme theories which was further revised and refined through a stakeholder consultation. Seven empirical studies were used for refining the initial programme theories. From these, we developed seven programme theories and a theoretical framework, with researchers independently involved in theming data and developing explanatory causal chains of context-mechanism-outcome. Although the review was intended to seek evidence from inpatient admission avoidance intermediate care schemes from high-income European countries, most of the evidence originated from a particular scheme in Norway.</p> Results <p>Three programme theories for explaining effectiveness related to referral to and utilisation of inpatient AAIC services: General practitioners’ (GPs’) positive/favourable perception of the care within inpatient AAICs; GPs’ confidence, security, and fulfilment of responsibility; and synergy and respect between healthcare providers. Two programme theories were related to quality of care: comfort and convenience for patients and an enabling working environment for nurses. Two programme theories were related to the cost of care: adaptive resources and payment mode. A causal framework for effective and efficient implementation and delivery of inpatient AAIC service was constructed.</p> Conclusion <p>This review informs policymakers and managers towards successfully adapting inpatient AAIC services to specific settings. Intended outcomes are achieved when an enabling environment is ensured for both service providers and users. Flexibility in resource use facilitates efficient organisation of services. More primary research with a focus on the identification and evidencing of mechanisms - of how and why inpatient AAIC services work - is necessary to further inform the design and delivery of such services in different contexts.</p>