Picture book reading can provide rich opportunities for learning across early development. In this chapter, the authors provide a conceptual model for understanding the ways in which children and caregivers typically read mathematical picture books and identify the ways in which books can be designed to promote mathematical learning. The model highlights two main components that influence whether a book will promote children's early mathematical learning: (1) the design of books themselves and (2) how readers use the picture books. From this, it suggests that mathematical picture books can be improved through intentional design to incorporate features that promote mathematics and through the strategic use of well-designed picture books by caregivers. This model can be used to guide the design of books, select among existing books that are most likely to align with evidence of educational effectiveness, and motivate future research on using books to promote children's early mathematics learning.