The fundamental question of objective versus subjective criteria in the establishment of regional systems in geography has long been debated. To address this conflict, the peninsular part of western France, known generally as “Brittany”, was chosen as a case study in regional methodology. The conflict between objectivity and subjectivity in regional analysis is considered and rational limits for the application of regionalizing techniques are suggested by factorial distributions. The physical, historical, cultural, and economic regional characteristics of Brittany and the manner in which these characteristics have set this region apart from the remainder of France throughout history are analyzed as well as how the range of the characteristics of Brittany commend themselves for consideration as significant regional determinants. A “Breton Index” is developed which applies various criteria to every canton in Brittany. The derivation and application of this “Breton Index” make a compelling case for the utilization of subjective criteria as the primary determinate for regional delimitation.