The burgus(Lat.)=bourg(Fr.)mentioned frequently in medieval texts of northwest France was a new settlement grafted in a nucleus of the existing one. The diversity of its from does not permit us to qualify it globally as either urban or rural. The term burgensis=bourgeois appeared originally in the meaning of inhabitant of this new wettlement. In recent years, bourg and bourgeois have been studied from the point of view of feudal development. In Normandy, there developed a tenure called burgagium=bourgage, which, generally thought to be an indicator of bourg/bourgeois, gave rise to L.Musset's skillful formula of the inseparable trinity of burgus/burgensis/burgagium. Nevertheless, two facts oblige us to reconsider this view. First, the earliest mention of burgagium is dated a century later than that of burgus/burgensis. Secondly, the propagation of bourgage was limited to Normandy. Beyond the Channel, the burgus=borough in the contemporary English texts is a settlement generally more urban than the French bourg. Here also, it has often been said that the burgagium=burgage was a tenure peculiar to borough. However, the earliest mention of burgagium concerns settlements not qualified as burgus. Moreover, it is very interesting that the appearance of burgagium in English documents was slightly earlier than in Normandy. This study is founded on a criticism of the rather loose conventional methodology, which tends to regard all tenures somewhat privileged as bourgage/burgage. To this end, the author attempts to trace the appearance and the diffusion of bourgage/burgage, by relying exclusively on the term burgagium in the documentation. Considering Normandy and England at the same time, her findings confirm for tboth regions a substantial discordance between the geographical or chronological distribution of the burgagium and of burgus/burgensis. The term burgagium was created first in northeast England, during the period of the systematic settlement of Normans under colonisation into this frontier area. It designated globally privileges that the inhabitants in the old great boroughs had progressively obtained. The intention was to grant them to recent settlements which needed immigrants ; the burgagium served as a device to attract new inhabitants. In the following stage, the burgagium was introduced into Normandy ; it was applied not to the great towns from the early Middle Ages, but to developing settlements, like in Ingland. In addition, the propagation of burgagium in both the regions can be interpreted as a phenomenon indicating the integration of social structure in the "Anglo-Norman Realm."