My work as a teacher educator and my research have been intimately entwined, so I derive questions and insights from what I see and hear of learners’ mathematics alongside my own experiences of doing mathematics. In this chapter I describe pathways towards my understanding more about how learners gain a sense of the concept of functions. Here I focus mainly on secondary school mathematics (ages 11 to 18) but my thinking influences how I work with teachers at all levels of school mathematics. My passion for mathematics, and experiences of learning and teaching it, colour everything I do in our field. The role of exemplification, particularly in how variations are presented in the public space of classrooms, have been central in this particular pathway.