Children think mathematically long before they start school. Before children start learning mathematics at school, they show informal understanding of many numeracy concepts. This is informal numeracy knowledge, that is, skills that children develop before starting school that do not depend on written mathematical notation (Purpura & Napoli, 2015). This review synthesises current research from neuroscience, psychology and education to highlight some key findings in the development of preschool children’s early numeracy skills. The review focuses on three areas: origins of preschoolers’ numeracy skills, important numeracy skills in preschoolers’ development, and connections between preschoolers’ numeracy skills and their later school achievement. The purpose of the review is to highlight a selection of relevant research findings. It is not intended to be an exhaustive review of the literature. The aim is to emphasise the significance of preschool children’s early numeracy development and to argue for the importance of fostering early numeracy in early childhood contexts.