Objective: The objective of this study was to identify and understand the health system contexts and mechanisms that allow for homeless populations to access appropriate healthcare when needed.

Design: A realist review.

Data sources: Ovid MEDLINE, embase.com, CINAHL, ASSIA and grey literature until April 2019.               

Eligibility criteria for selecting studies: The purpose of the review was to identify health system patterns which enable access to healthcare for people who experience homelessness. Peer reviewed articles were first identified through a systematic search, grey literature searching, citation tracking and expert recommendations. Studies meeting the inclusion criteria were assessed for rigour and relevance and coded to identify data relating to contexts, mechanisms and/or outcomes.

Analysis: Inductive coding was used to generate Context-Mechanism-Outcome configurations which were refined and then used to build several iterations of the overarching programme theory.

Results: Searching identified 330 review articles, of which 24 were included. Additional searching of grey literature yielded 50 records of which 12 were included. An additional 11 grey literature and primary sources were identified through citation tracking and expert recommendation for a total of 47 included sources. The analysis found that healthcare access for populations experiencing homelessness is improved when services are coordinated and delivered in a way that is organised around the person with a high degree of flexibility and a culture that rejects stigma generating trusting relationships between patients and staff/providers. Health systems should provide long-term, dependable funding for services to ensure sustainability and staff retention. 

Conclusions: With homelessness on the rise internationally, this study will inform health systems policy-making and implementation. It contributes to our understanding how healthcare systems can be more accessible for populations experiencing homelessness by providing long-term stable funding, promoting inclusive cultures and limiting stigma. Health systems should be flexible, timely and connected.