CONTEXT: Although cereal–legume intercropping is a recognized approach to improve crop production sustainability, its uptake on European commercial farms remains slow, due to numerous questions raised by the introduction of intercrops in a cropping system. Co-design workshops allow multiple scenarios to be explored without risks. They favor identification of consistent answers to complex problems, considering local conditions and constraints. OBJECTIVE: We present Interplay, the serious game we created to support players’ exploration of intercrops by designing a wide-range of cereal–legume intercropping scenarios in given cropping system contexts and assessing eight ecosystem services provided by intercrops, i.e., intercropped cereal and legume yields, cereal protein content, nitrogen supply to the following crop, impact on soil structure and weed, insect and disease control. METHODS: Interplay aims at being used with groups of farmers and their advisor or students and their agronomy teacher. The game includes a game board and cards to design intercropping scenarios defined by: (i) the cropping system and field context; (ii) the farmers’ objectives when introducing an intercrop; (iii) the species to associate and (iv) the crop management. A computer model assesses the ecosystem services provided by the intercropping scenario designed on the game board. The players compare these results to their objectives and to sole crop performances and, if necessary, adjust the scenarios. The players are guided through the design process by a facilitator. RESULTS AND CONCLUSIONS: In the context of the Covid-19 pandemic, we used the game with 70 French agriculture students divided into six groups to design intercropping scenarios improving nitrogen supply to the following crop in a rotation. Students designed scenarios that improved nitrogen supply compared to the initial sole crop, yet cereal yield decreased more than the farmer desired. Guided by the facilitator, students reconsidered the cropping system to improve nitrogen supply at the crop rotation level. Interplay is an interactive tool used to stimulate players’ creativity by exploring intercropping scenarios and providing salient, credible and legitimate assessment of the ecosystem services provided. It also promotes knowledge sharing on intercropping and allows redesigning the cropping system completely. Students and teachers who used it declared that it helped enhance their knowledge on intercrops. SIGNIFICANCE: Interplay is the first serious game suited to develop the practice of intercropping. It is currently available for cereal–grain legume intercrops sown simultaneously in a random pattern under French soil-climate conditions, but could be adapted to other countries and intercrops.