He graduated with a thesis on The economic life of the abbey of Clairvaux, from its beginning to the sixteenth century (1949), and passed the teaching exam (agrégation) in history.
In the 1970s, he began to focus his research and publications on the peasantry and feudalism (a term he refuses to use) between the eleventh and thirteenth centuries.
According to Robert Fossier, the grouping of the village in the north of the French kingdom was due not only to incastellamento, but rather to lordly initiative in general.
In his latest book, Ces gens du Moyen Age (translated as The Axe and the Oath: Ordinary Life in the Middle Ages), Robert Fossier deemphasises the aspect of medieval society which we are most familiar, the aristocracy, in order to concentrate on that less spoken-of aspect, the people.
[2] The works of Robert Fossier have gained considerable fame (including at least 37 translations in North and South America, Japan, Germany, and Great Britain).