This discussion of theories of writing instruction arises from the context of teaching research writing to postgraduate students for whom English is an additional language. However, given the present diversity of the student body in all tertiary writing courses(as a result of the democratization and internationalization of higher education), it is argued that a principled evaluation of theories of writing instruction that places the academic literacy needs of the student writer as central is relevant to the wider field of tertiary writing instruction. As a basis for this review discussion, the paper proposes that student writers need to develop their knowledge and skills in three areas: discourse competence; identity and voice (within a specific academic community) and critical competence, and that the development of these three areas of writer competence is loosely sequential. The paper reviews four different theories of writing instruction is terms of their capacity to advance these areas of writer knowledge and skills; they are the process writing, post-process, genre-based and critical literacies approaches. The paper argues that a critical understanding of these theories and the ways in which they underpin currently available materials and teacher practice is essential if teachers are to be able to provide a well-argued rationale for assumptions, knowledge, skills and ideologies that underpin their courses.