Most market-garden farms that have converted to organic farming (OF) in the last few decades in France are small and diversified. Larger farms usually specialize in a few vegetable species and frequently face technical and economic problems when they convert to organics. Diversifying production may be a means of increasing sustainability due to larger crop rotations and varied marketing outlets, but it has various implications on farm management, especially labour organization and marketing. In the present study, we examined how an acceptable degree of species diversification can act as a lever to develop organic vegetable production by combining sociologist and agronomist points of view. Multidisciplinary surveys of 30 market-garden farms varying in usable surface area and degrees of crop diversification were carried out. Consequences on crop management, labour organization and skills, and marketing implications were described, and farm sustainability was assessed. Specialized farms of the sample had a rather industrial organization of labour and marketing and benefited from economy of scale to produce vegetables. But in the long term, they may suffer from low agronomical sustainability because of narrow crop rotations and intensive crop management. Diversified farms were more sustainable according the criteria studied, but they suffered from the extremely complex management of cropping systems. These results are discussed on both the farm and territorial levels. Collective marketing initiatives and social networks might help reach an acceptable degree of species diversification at the farm level. Potential innovative organizations are identified, which could facilitate the transition to OF.