Despite a proliferation of research into academic writing and the availability of a number of guides to writing, little attention has been given to the means of supporting students striving to reach the level of proficiency in English expected from graduates in their respective fields. Our study aims to explore the prevalent problems in writing in English encountered by Finnish university students. In doing so, we revisit the notion of communicative competence in order to gain deeper perspectives on academic/scientific written discourse and apply these to classroom practice. The corpus on which we draw comprises academic/scientific texts produced by students of biochemistry and architecture in their field-related English courses. We begin by surveying and categorising recurrent problems observed during course work. Then we establish a matrix of the most salient problems on various levels, including macro-textual aspects, micro-structural concerns such as morphology, style, register and syntax, as well as metalinguistic issues. Using this matrix, we systematically analyse a sample of the corpus to determine the prevalence of the problems. Further, building on earlier models of competence, we propose a model which consists of six competence areas, the significance of which vary according to the purpose of the text, the learning needs of students or the teacher's didactic purpose. The model can be used for raising learners' awareness of what academic/scientific writing entails, and for analysing texts in order to diagnose students' difficulties and inform course design.