BackgroundGypsies, Roma, and Travellers (GRT) are less likely than the general population to access health services. The reasons are multiple, complex, and interlinked, and they exist at individual, provider, health system, and national levels. We report on two studies that explore GRT use of UK health services. Study 1 aimed to investigate barriers to, and facilitators of, immunisation, and identify interventions to promote uptake. Study 2 aimed to explore approaches that facilitate engagement and trust between GRT and health services, with maternity, early years, and child dental health services as exemplars. MethodsStudy 1, completed in 2016, involved in-depth interviews with 174 GRT from six communities and 39 service providers in Scotland and England, and intervention mapping and co-production workshops with 76 participants to prioritise interventions. Study 2, to be completed in 2017, involves systematic reviews and a realist synthesis; online consultation with 196 UK-based stakeholders; case studies involving interviews and focus groups with 44 GRT, 54 health-care professionals and 13 third sector staff in Scotland and England; and cross-sectoral workshops which will refine policy recommendations. Qualitative and quantitative analysis identified barriers and facilitators to receiving health care; and approaches to enhancing engagement and trust in health care. Ethics approval for study 1 was granted by National Research Ethics Service Committee Yorkshire and The Humber, Leeds East, and for study 2 by the NHS Health Research Authority East Midlands, Leicester Central Research Ethics Committee (16/EM/0028). FindingsBarriers to health care included discrimination, economic disadvantage, differences in cultural interpretations, language, and health literacy. Facilitators included trust in health professionals and intergenerational change towards valuing health services. Approaches to enhancing engagement included specialist workers and named professionals for GRT communities, cultural training for professionals, and tailored or flexible systems. Facilitating the research depended on collaborating with trusted gatekeepers, and both studies used co-production methods to ensure that study recommendations are grounded in practice realities and acceptable to stakeholders. InterpretationThe findings provide advice for practitioners and policy makers engaging with GRT people, as well as insight on supporting other marginalised populations. Exploring the experience of GRT, service provision, and policy offers a substantiated account enabling public health to reflect on success or otherwise of interventions aimed at tackling inequalities. FundingStudy 1 was funded by the National Institute for Health Research Health Technology Assessment Programme (12/17/05). Study 2 is funded by the Department of Health Policy Research Programme (Enhancing Gypsy/Travellers' trust: using maternity and early years' health services and dental health services as exemplars of mainstream service provision, PR-R8-0314-24002).