Introduction:Loneliness and social isolation among older adults (≥65) are an emerging issue of public concern, associated with increased morbidity and mortality. Today there is no systematic intervention developed, implemented or evaluated in Sweden addressing loneliness. The overall aim for this project is to develop, test and refine a person-centred Swedish model for social prescribing (SPiS), and to assess whether and how it reduces loneliness, promotes health and improves well-being among older adults.Description:The focus will be to develop, culturally adapt, evaluate and refine the SPiS model. Following the sequential structure of realist evaluation in three consecutive phases qualitative and quantitative data along with subsequent analysis methods will be collected and utilized. The project will provide knowledge of what works with the social prescribing model, for whom, in what conditions and why, in relation to loneliness, health and well-being among older adults.Discussion:SPiS has the unique position of providing initial knowledge regarding how to reduce loneliness in the Swedish context. However, evaluation is complex as this research goes beyond the unidimensional question “Is it working?”.Conclusion:Developing, implementing and evaluating such a complex program needs systematic and close evaluation.