Spatial planning and territorial development are complex areas whose laws and regulations are country-specific. These are not the first subjects to be shared cross-border at risk of great difficulties. Yet their impact on everyday life is very important (housing, economy, services, mobility, environment...). In territories where the border event is old and more solid, they can be tackled to solve the obstacles that hinder good coordination between neighbours (management of natural spaces, infrastructure projects, economic and commercial developments...). C is the objective of this Franco-German experimentation (MORO) in the form of two pilot projects dealt with in parallel and in coordination. Its purpose will not be to lead to agreements on content but to work on the processes that make it possible to strengthen the contractualisation of cross-border territorial projects. The method used will be that of “Planspiel” or simulation. It should make it possible to better understand cross-border decision-making processes in the field of planning and thus overcome barriers at borders, in line with the objectives of the draft European regulations for Interreg financing (CTE). The conclusions will be forwarded to the Cross-border Cooperation Committee (CTC) of the Treaty of Aix la Chapelle in order to be able to endorse the solutions outlined.