In this book I bring together considerations I have made and published about the meaning of symbols for learning in general. And since maths is made up of symbolic systems. I also talk here, in a clear and accessible way, about the Theory of Semiotic Representation Registers as a way of understanding, specifically, the learning of maths; since it was conceived to bring contributions to the understanding of how the learning of this discipline is processed cognitively and can help teachers and researchers working in this field of knowledge.