This report is part of the BONUS BALTSPACE project and is focused on challenges for policy and sector integration in Baltic Sea marine spatial planning (MSP). The main objectives have been to identify concrete coordination problems, to analyse why they have emerged and to discuss possible remedies. It is based on selected aspects extracted from case studies carried out in this project related to the development of regional MSP approaches in Denmark, Germany, Latvia, Lithuania, Poland, and Sweden and on an additional case study on the HELCOM-VASAB Working Group on MSP. To facilitate the analysis of vertical policy interactions between institutions at different levels as well as of horizontal interactions over sector and country borders, an analytical framework was constructed. This framework consists of two main components; (a) institution-driven coordination where institutions such as global treaties, the EU, regional organisations, and state authorities provide boundaries for decisions taken at lower levels and (b) benefit-driven coordination capturing horizontal coordination across sector and country borders.