This special issue comprises five studies which vary in their focus and mathematical content, yet they all share an underlying communicational theoretical framework--commognition. Within this framework, learning mathematics is defined as a change in one's mathematical discourse, that is, in the form of communication known as mathematical. Teaching can be defined as the communicational activity the motive of which is to bring the learners' discourse closer to a canonic discourse. Reading the five research articles interconnected via their shared theoretical infrastructure has the potential to further develop insights about various aspects of teaching and learning mathematics.