This theoretical article considers the relation between the use of digital tools in the teaching and learning of mathematics and the development of students’ identities as mathematical writers, within their upper secondary school education. The theoretical outset is the instrumental approach in mathematics education, which studies how students appropriate digital artifacts as tools. We argue that the focus on epistemic and pragmatic mediations, which has long been prevalent within this approach, can benefit from being augmented with a focus on the students’ identity work. The interest for students’ identity work in relation to their use of digital tools in mathematics grew out of a longitudinal ethnographic case study of Danish upper secondary students in the subject of mathematics. Using data excerpts from this study we provide empirical examples of an identity perspective on the use of digital tools in mathematics education and discuss possible ways to incorporate “identity” and ”identity work” in the instrumental approach.