The purpose of this article is to provide strategies for recognizing meaningful mathematics in common play contexts in early childhood classrooms and to offer suggestions for how teachers might intervene in these moments to help children attend to the mathematical ideas embedded in their play. In particular, the author's focus on the concepts of composing and decomposing, which are fundamental concepts in early mathematics and essential to the understanding of big ideas in both number and geometry. Through a yearlong study of a rural public preschool in Georgia, the author's found three common play contexts to be particularly rich sites for children's exploration of composing and decomposing: the block area, the puzzle table, and the doll corner. This article describes the mathematics embedded in each of these contexts with the goal of helping early childhood teachers to recognize and highlight similar mathematics in play.