The authors present and discuss the conceptual and technical design of the game Marine Spatial Planning (MSP) Challenge 2050, developed with and for the Netherlands’ ministry of Infrastructure and Environment. The main question in this paper is: What constitutes the socio-technical complexity of marine areas and how can it be translated into a simulation model for serious game-play with marine spatial planners? MSP Challenge 2050 was launched in March 2014 in a two day session with twenty marine planners from six countries. It aims to initiate and support MSP in the various Atlantic regions by bringing policy-makers, stakeholders, scientists together in a ‘playful’ but realistic and meaningful environment. In the North Sea edition of the game, six countries make and implement plans for this sea basin over a period of 35 years, with cumulative effects of their sectoral and national decisions emerging. The authors conclude that the combined and iterative use of complexity modelling and gaming is effective from the perspectives of design (development of a MSP model), research (insight acquired on MSP) and policy (policy-oriented learning and analysis for MSP). Further development and global dissemination of MSP Challenge 2050, as well as research and data collection, is foreseen.