Vowel nasalization and the subsequent development of these nasalized vowels constitute one of the most intensively studied areas in French historical phonology. Despite this attention, however, the set of problems associated with these phenomena is not exhausted. I will argue here, for example, that nasalization in French provides evidence for the crucial role of allophonic information (redundant phonetic detail) in initiating and conditioning phonological regularities, thus violating the local determinacy constraint (Chomsky 1964) placed on the phonemic level of representation. The same evidence also illustrates an infrequent type of historical change, and reinforces the impression that much fertile ground remains to be tilled in this particular field.