This paper analyses challenges and enablers for integrating a transboundary land-sea interaction (LSI) perspective into marine spatial planning (MSP) practice as experienced in the Baltic Sea Region. Collaborative research results from the Pan Baltic Scope project indicate that LSI remains an amorphous concept, particularly within a transboundary MSP context. Difficulty lies in bridging planning practices across land and sea and between varying uses, administrative settings and governance functions. Addressing LSI requires capacity, time, resources, awareness, reflection, and forums for collaborative learning across sectors and governance levels.