Understanding mathematics teaching and learning “in their full complexity”When I did my master’s in mathematics education in the 1980s in Copenhagen, Denmark, my professor, Bent Christiansen, used to say that the aim of mathematics education research is “to understand mathematics teaching and learning in their full complexity and contribute to their further development” (personal communication). Except for the somewhat absolutist connotations of the way he phrased it, I think most in our field today would agree with Christiansen’s intention: we are to develop comprehensive understandings of the problems of mathematics teaching and learning, and the ambition is, at least in the long run, to support the development of institutionalised teaching–learning practices.