Within the historiography of the ‘Angevin empire’ the subject of the duchy of Brittany as a province within that ‘empire’ has been all but overlooked. Nevertheless, no general survey of the ‘Angevin empire’ or of the reigns of the Angevin kings can altogether ignore Brittany, since it was one of the several territorial principalities which came under the domination of the Angevin kings of England during the reign of Henry II. In need of some concrete piece of evidence from Brittany in this period, historians have gratefully embraced a single act of Angevin government, the so-called ‘Assize of count Geoffrey', ‘count Geoffrey’ being the younger son of Henry II who became duke of Brittany by marriage in 1181. This to the extent that, in more general works on Brittany or the Angevin empire, the promulgation of the ‘Assize’ is often the only aspect of Duke Geoffrey's reign to be noted, usually uncritically. In contrast, the ‘Assize’ is not well known amongst that vast majority of legal historians whose primary interests lie outside twelfth-century Brittany, but who would be better qualified to place it in its historical and legal context. There are numerous editions of the ‘Assize', mostly after the ‘Vitre'’ version published by Pierre He'vin in 1684. Those most accessible outside France are the editions published by Marcel Planiol and more recently in the collected charters of Duke Geoffrey.

There are in fact other acts of Angevin government from Brittany, in the form of charters and writs, and there is also contemporary evidence for more such acts which have not survived. The ‘Assize’ is, in diplomatic terms, almost indistinguishable from other charters of Duke Geoffrey, but it is unique in that the provisions of the ‘Assize', which deals with succession to baronies and knights’ fees, retained the force of law in Brittany until the French Revolution. Consequently, the existence of the ‘Assize’ was common knowledge amongst the cadre of ancien régime legists and administrators such as Bertrand d'Argentre’ and Pierre He'vin whose scholarly endeavours produced the first modern histories of Brittany. In contrast, the other Angevin acts remained buried in the archives and cartularies of the monasteries, material of purely antiquarian interest. Not only was the ‘Assize’ well known to these scholars, but it was of great interest to them, not so much for its substance as for its form.