This case study documents the disciplinary writing practices of a non-native English-speaking (NNES) postgraduate student in the field of aeronautics and astronautics engineering at an American university. It discusses how the process of learning to write in a specific discipline involved textual mentorship from disciplinary texts, negotiation with and feedback from the thesis advisor, and the writer's investment in disciplinary knowledge, writing expertise and discourse knowledge. In this case study, it was found that the co-authoring opportunity with the advisor was the most critical enculturation task, facilitating disciplinary writing practices. The revisions made across drafts of research abstracts revealed the multiple, authoritative roles the advisor played-as a language shaper, a content expert, and an experienced disciplinary writer. The level of textual participation also reflected the writer's degree of ownership of his texts. Becoming familiar with content-specific knowledge and discourse norms, the postgraduate writer took increasing responsibility in the practices of writing and publication, and made increasing contributions to his final written texts.