Nursery education, particularly in terms of mathematics, has come a long way in a short time. But what principles or knowledge can now be used to decide what is or is not good practice? It therefore seems timely to look at theory and research concerning teaching mathematics to young children, to try and establish some principles and guidance as to what might constitute good practice in the Foundation stage, but particularly with regard to the youngest children, the 3- and 4-year-olds. To take a traditional early years approach, one way of looking at what is appropriate is to consider what is known about how children learn, in terms of cognitive, physical, emotional and social aspects, and then to look at the implications for teaching strategies. The focus of this article will be particularly in terms of number, since this seems the most problematic area, which is new to many early years practitioners and which particularly requires adult support. In this article, the author will attempt to summarise current thinking based on theory and research, in order to establish a framework of pedagogic principles that can be used to evaluate activities, such as those of the national numeracy strategy.