The global debate on food security and the kinds of farming systems that could prove economically and ecologically sustainable has focused overwhelmingly on small family farms versus large commercial farms, with little attention to alternative models based on farmer cooperation. France offers a significant but internationally little recognised (and under-researched) model of group farming—the GAEC (Groupement Agricoles d’Exploitation en Commun)—based on farmers pooling land, labour and capital. This model is of considerable contemporary interest for both France and other countries. Catalysed by a 1962 law, GAECs accounted for 7.6% of farms and 15% of agricultural adult work units in 2010, but their incidence varied greatly across regions. Using data from the French agricultural census and other sources, this paper identifies the factors (economic, ecological, social and demographic) underlying this regional variation of GAECs (and comparatively of EARLs—Exploitations Agricoles à Responsabilité Limitée—another type of group farm introduced in 1985). Regions with a higher incidence of group farms are found to be those with greater economic equality, local ecology favouring labour-intensive animal breeding, social institutions that promote community cohesion, and higher proportions of agricultural graduates, among other factors. The paper not only illuminates the contexts favourable to the emergence of group farming in France, but also points to the conditions under which farmer cooperation could take root elsewhere, thus breaking new ground on an issue of substantial policy relevance.