Since the 1960s there has been a global trend toward specializing and intensifying farming systems in order to produce more food. However, harmful environmental consequences have been recognized. Integrated crop–livestock systems (ICLS) are now being reconsidered as a means of improving farm and land sustainability. We suggest that understanding interrelations of ICLS to achieve sustainability requires scrutinizing the way farmers exploit them to adapt their farming system. We used six different case studies covering maritime and semi-maritime regions of France (beef and dairy + crop systems) to describe factors influencing production, environmental, and socio-economic considerations for change in farming practices. Farm surveys and analysis of farmers’ practices and farm time-course of change were framed within the European farming system approach. Transition in the medium-term pointed out new interactions at stake between crops and livestock when farmers developed adaptation to climate changes, introduced grassland in contrast to the general trend of specialization and enhanced feed self-sufficiency. In the medium- and short-term, multifunctionality of crops and crop rotation adjustments, as well as regulation of cropping systems by livestock classes are the main levers of system flexibility. We showed how ICLS increased sustainability and began to notice the positive effects of farm collaboration. Further research is needed in partnership with additional stakeholders to support sustainable development of agriculture at the landscape level.