In Sweden, the activities initiated to promote return to work (RTW) are performed in parallel by four different public organisations: the health services, the social services, the employment and the social insurance authorities. The aim was to gain deeper understanding on the experiences of professionals involved in cooperative projects aimed at promoting RTW among unemployed sickness benefit recipients. Qualitative analyses were performed of transcribed data from interviews of professionals participating in cooperative projects. First, the analysis identified that the daily collaboration on the same cases enabled development of good relationships and cooperative competence, which improved the contact with clients. Second, the cooperative projects made it possible to include only clients perceived motivated for RTW measures. Third, the closer and more frequent interaction with clients proved to be constructive in that it facilitated recognition and mobilisation of strengths and abilities. Fourth, the differences in rules and regulations between the social insurance and the unemployment insurance standards were often perceived to induce problems, for example, on how to assess the work capacity of clients. The assessments of work capacity represent important and complex tasks that professionals must perform without having access to either scientific knowledge or consensus agreement on which to base their decisions.