Background and Objectives: Social inequalities in health are complex and vulnerable people often experience higher unmet needs and lacking coherence when seeking healthcare. They therefore require cross-sectoral initiatives. Literature argues that healthcare organization is an important but overlooked determinant of social inequalities in health, as health systems buffer or amplify structural and individual health determinants. The Flexible Assertive Community Treatment (FACT) model offers integrated healthcare access to people with severe mental illness, through interprofessional teams across health and social services. This study aimed to assess the organizational contexts that shape the implementation of this model of integrated care. Methods: The study includes a document analysis of political and administrative documents, and semi-structured interviews of managers and healthcare professionals in three municipalities. The study applied the theory of the Organizational Fields to assess the organisational contexts in implementing the FACT model. Results: Implementing FACT was challenged by the co-existence of different contexts across health and social care and across national and regional levels, for example by having conflicting legislation in the health and social field. These contexts make conflicting demands on intersectoral coordination, where person centered care is for instance bound by different norms and values at each level. Therefore, the successful implementation of FACT comes to depend on strong local cultures of collaboration that translate and transfer these demands into an integrated, local organisation of FACT. These collaboration cultures however differed across the municipalities, and some therefore appeared more successful in implementing FACT than others. Conclusions: Implementing an integrated care model as FACT might become challenged by the complex and different organizational contexts vertically, at each level, and horizontally, e.g., between municipalities. The assessment of these contexts is key to identifying possibilities and limitations for a successful implementation. This knowledge may in turn reduce social inequalities in health by providing more accessible and coherent care.