Background <p>Integrated care uses inter-professional and inter-organisational collaboration to ensure quality care for those with complex healthcare needs. Whilst inter-organisational collaboration is seen as a facilitator of integration, it has its own complexities and challenges. This study sought to investigate barriers to and facilitators of inter-organisational integration between the partnered organisations of an integrated care initiative in Luton, UK, as perceived by healthcare professionals.</p> Methods <p>Face to face semi – structured interviews were conducted between November 2019 and March 2020 with twenty service providers of an integrated service for physical and mental health. Thematic analysis was used to explore the experiences and perceptions of service providers on the integration of healthy lifestyle and mental health services of “Total Wellbeing Luton”.</p> Results <p>Five primary themes were identified: (1) Culture, (2) Communication Structures, (3) Strategic alignment, (4) Workforce dynamics, and (5) Expectation and reality of the integration. The majority of the identified themes reflect factors that facilitate or impede the integration between the participating organisations. Excellent relationships between healthcare professionals and staff’s motivation have been identified as facilitators to inter-organisational integration, while high staff turnover, lack of shared IT system and absence of co-location have been identified as barriers. Also, a theme reveals that often there was a discrepancy between the expected and the actual implementation and outcomes of integration.</p> Conclusions <p>As a part of a larger evaluation programme, this study attempts a comprehensive understanding of the inter-organisational integration in the specific context of Total Wellbeing Luton. The findings and recommendations can support the inter-organisational integration of current and future integrated care initiatives in the UK and elsewhere.</p>