In order to design cropping systems reconciling crop production, biodiversity and reduced herbicide use, we organized participatory workshops with farmers in the Champagne region (North-Eastern France). Methods combined cropping-system prototyping by farmers, expert opinion and models. In a first meeting, farmers determined their objectives and constraints, and chose a reference system existing in one of their farms (oilseed rape/winter wheat/winter wheat/spring barley heavily infested by autumnal grass weeds). In a second meeting, two sets of prototypes were designed by two separate groups, using the Mission Ecophyt’eau® tool (https://ecophytopic.fr/pour-aller-plus-loin/outil-mission- ecophyteaur) as support. The reference and the prototypes were evaluated in terms of (1) technical feasability from farmers’ and scientists’ expertise, (2) weed harmfulness for crop production and weed contribution to biodiversity with FlorSys which simulates crop and weed growth and reproduction in cropping systems at a daily time step over several years (Colbach et al., Weed Res 2014), and (3) economic, social and environmental sustainability with the DEXiPM (Pelzer et al, Ecol Indicators 2012) model. Steps 2 and 3 were carried out after the meeting. At a third meeting, these results were presented to the farmers who continued improving the prototypes, using the DeciFlorSys model which includes decision trees to guide farmers during cropping-system design and a fast calculator estimating weed harmfulness and biodiversity of cropping system prototyes (Colas et al., Eur J Agron 2020). Both prototypes presented increased crop diversification, introducing legumes and other broadleaved crops, crop mixtures and cover crops. Prototype A was based on reduced tillage and annual crops only. Prototype B also included multi-annual lucerne and optimised both tillage and mechanical weeding. Both prototypes reduced weed harmfulness for crop production (yield loss, harvest contamination, field infestation) and herbicide use intensity (approx. -60%) compared to the reference system. Prototype B also improved weed-based trophic resources for carabids and pollinators. The best solution was a suboption of prototype B replacing most of the herbicides by mechanical weeding, dividing yield loss by nearly two compared to the reference and improving biodiversity by 5-10%. The workshop participants appreciated the knowledge on agroecosystem functioning and the complementarity of models: DeciFlorSys allowed a direct evaluation during workshops, FlorSys produced a detailed diagnosis of the technical and meteorological causes of the cropping systems’ performance and DEXiPM assessed working times and economic viability of the prototypes. Following the workshops, some participants invested in new implements for mechanical weeding and introduced more spring crops into their rotations.