In Chapter 2 we discussed how neurologists and psychologists have proposed that we have a sense of numerosity. Although not a sense in the same way as sight or hearing, it provides us with a foundation and processes through which we develop the whole of our mathematical knowledge. The proposals that they describe are of great interest to those of us who are working with children who are at the early stages of learning. To understand their learning needs we need to take ourselves back to learning experiences that we take for granted, for example the powerful sense of ‘one’ that comes from holding a single item in one palm, and how different it is when both hands are occupied – three is too many to hold, and is therefore a beginning of the concept of ‘many’.