Social Semiotics, based on the work of the linguist Michael Halliday, emphasises the ways in which language functions in our construction and representation of our experience and of our social identities and relationships. In this paper, I provide an introduction to the theory and its analytic tools, considering how they can be applied in the field of mathematics education. Some research questions that may be raised and addressed from this perspective are identified. An illustrative example is offered, demonstrating a social semiotic approach to addressing questions related to construction of the nature of school mathematical activity in writing produced by secondary school students.