A large part of building development for housing and other activities is concentrated today in discontinuous spaces located on the outskirts of urban centralities. This dynamic of diffuse urbanization is part of an international trend and one of the features of the « post-suburban » world (Phelps & Wu, 2011). In cross-border regions, regulation of diffuse urbanization faces specific challenges due to diverging planning systems and cross-border mobilities (Buitelaar & Leinfelder, 2020 ; ESPON & Luxemburg University, 2010). The aim of our study is to highlight the place of farming activities in the regulation of diffuse urbanization in the context of a cross-border region characterized by important urban sprawl and challenges for farmland preservation : the French-Belgian border. We propose to take into account the variety of developments induced by farming activities : housing needs for farmers, building projects linked to conventional agriculture but also innovative diversification activities (on-farm processing and marketing, agritourism) (Perrin et al., 2020). We follow a sociological approach, focused on the implementation of planning regulations at the local level not only by planning authorities, but also by the various stakeholders of the land tenure system (Dongmo Zangue et al., 2022 ; Idt & Pellegrino, 2021 ; Le Bivic & Melot, 2020 ; Holtslag-Broekhof et al., 2014). This inquiry is implemented within the frame of the research project « Gertrud » on « Cross-border Management and Regulation of Diffuse Urbanization », funded by the French national research agency. Under this project, several case studies are currently conducted in cross-border regions with France, Belgium, Luxemburg, Germany and Spain. The objectives of the research project are to understand the difficulties encountered by public and private actors in planning the production of diffuse urbanization and to identify barriers as well as innovative practices, when facing with different planning systems and competing land uses in a context of cross-border areas. The presented research focuses on a case-study in French-Belgian border areas, especially in the peri-urban surroudings of the Lille conurbation. The inquiry is based on semi-structured interviews conducted in France and Belgium with local stakeholders involved in the management of farmland and land-use : local planning authorities, farmland management agencies, farmer unions and NGOs, local bodies in charge of cross-border cooperation. Our first results show that differences in the regulation of farming activities in urban planning between both countries, but also competitions for access to farmland (due the lower price levels in France) may explain some dynamics of diffuse urbanization in the outskirts of conurbations. This research could contribute to new insights on cross-border urbanization by underlining the necessity to integrate farming activities in the planning of suburban areas.