This paper attempts to capture some of the breath of frameworks and models on mathematics teachers’ knowledge in order to identify central lessons we have (not yet) learned from past and current approaches in theorizing and conceptualizing a knowledge base for teaching mathematics: there are accounts of the complex and multidimensional nature of teachers’ knowledge but no accounts as to the reorganization of dimensions of teachers’ knowledge in order to be more consistent with a constructivist view on learning and teaching; there are accounts of what teachers’ knowledge is about but no accounts as to a structural description of teachers’ knowledge. The paper highlights several unsettled issues of this research field and certain profitable directions for advancement.