During the early days of the French regime, common pastures were established on a third to a half of all the seigneuries in the St. Lawrence valley. Only a few have survived and it seems that besides the five commons in the lake St. Peter region very few are still in existence. Among the factors that contribute to explain the survival of these commons, the more obvious ones appear to be related to the local natural environment. The common pastures of lake St. Peter are located on low grounds easily covered by the spring floods. As a result they benefit from natural fertilisation and, because of their generally insular position, only need to be partly fenced. However, the historical documents concerning common pastures in Québec province indicate a great number of legal disputes between the seigneurs (in pre-conquest days) or the corporation, on the one hand, and the censitaires or farmers making use of their rights on the other. Indeed, these particular commons appear to have been marred by a long series of disputes generally related to problems of the natural environment. The farmers have always complained about the poor quality of the pasture and the inadequate drainage System of the fields. These are not the only problems related to the spring floods, for even the limited fencing heavily damaged by the moving ice blocks tumbling down the St. Lawrence. If such problems have contributed to the abandonment of other commons, why have the commons of lake St. Peter — where these problems are apparently even more frequent — survived ? The commons of lake St. Peter continue to play an important economic role. Every spring nearly three hundred farmers, from sixty miles around, lead nearly three thousand cattle, horses and sheep to these pastures. The perennial character of these commons cannot be explained solely by the relative advantages of the natural pastures in the low regions bordering the lake. Reasons of an economic nature and even perhaps of a socio-psychological nature, particular to this region, contribute to explain the survival of such original but « outdated » forms of agricultural land use. Survey research, already being carried out among the users, should help solve this question.