Pretend play is an important, universal activity of early childhood, but research to date contains multiple inconsistencies in definitions and measurement of pretend play. To begin to resolve this issue, we conducted a first study of the multiple different behaviors of pretend play in the preschool years (3-5 years), and investigated their developmental progression. Pretend play can be defined by five core behaviors, theorized to develop in this order: object substitution, attributing pretend properties, social interactions, role play, and metacommunication. We created a new observational measure to capture all five simultaneously for the first time, and used this measure in 34 hours of naturalistic observation of preschoolers (N = 73) engaged in play. Children's age was a significant, positive predictor of engagement in the higher-level pretense behaviors (social interactions, role play, metacommunication), and of engagement in multiple behaviors simultaneously. This study provides initial support for the theorized developmental progression of pretend play and provides a framework for future research.