This article presents an investigation into the socio-interactional nature of learner autonomy in language learning groups. The study is situated in the context of a mobile phone video project with 13 Mexican adult learners of German as a foreign language (GFL). The aim was to examine autonomy, heteronomy and participation in L2 classroom negotiations in a group work situation. These constructs have been shown to be highly influential in second language learning in an institutional context (Little, 2000; O’Leary, 2014; Schmenk, 2008; Thornbury, 2011). Decision-making episodes of three project groups were examined from an interactional, participational and sequential point of view. The analysis offered both an etic and an emic perspective on L2-group negotiation processes and allowed for the detailed reconstruction of collective and cooperative participation mechanisms. It unveiled a strong link between individual interaction styles, different types of participation, group discourse patterns and the display of group autonomy and/or personal autonomy. These findings inform an empirically grounded theoretical model of group autonomy in the L2 classroom, which will be introduced in this paper.