This paper analyses how the mathematical knowledge needed by a teacher has been described by several mathematics educators, all based on Shulman's notions of Subject Matter Knowledge and Pedagogical Content Knowledge. In particular, it looks at the notion of Mathematics Knowledge for Teaching, as elaborated by Ball and her research group. It then shows how a strong theoretical framework, such as Chevallard's anthropological theory of didactics, helps to analyse the mathematical knowledge and skills needed by a mathematics teacher in order to teach mathematics in a given institution. Finally, it provides a new description of Mathematics for Teaching, merging mathematical and pedagogical aspects, and it explains how this has been used in teacher training in Mozambique.