This chapter develops a practice-based approach to the documentation of an endangered language in a bilingual environment. I present the different axes of documentation of the different profiles of speakers, and the methodology for their elicitation. I address the documentation of dialectal variation and emergent varieties of Breton, for which I provide an inventory of the linguistic varieties in the 21st century. The dialects include the traditional dialects, which are attached to a geographic territory (geolects), and Standard Breton, which is not. Other linguistic varieties include registers, or forms characteristic of learners of Breton. All Breton speakers master another language, usually French. Some master several Breton dialects, including Standard Breton. For each variety, some speakers are native speakers, others learned Breton later (L2). Native speakers of all ages show some form of lexical diglossia, with characteristics of a heritage language, i.e., a native language acquired and practised with some form of impoverishment of the input. Modern speakers vary in proficiency. They form a spectrum that spans from, at the one end, proficient everyday speakers with occasional thematic code-switching to French to, at the other end, silent speakers who understand a single Breton variety. I mention for each profile of speakers some characteristics of their linguistic productions, with reference to acquisition and attrition studies.< Réduire