When does comprehension begin? This article addresses the question, and will help early childhood and elementary literacy educators understand how young children's comprehension, or meaning making, begins prior to conventional reading and emerges over time. Field note, video, and interview data were compiled during a three-year longitudinal study on emergent comprehension in children from age 2 to 5. Four phases--book as prop, book as whole, book as script, and book as text--detail how a group of 12 children used books during child-initiated events (e.g., play, pretend reading). Semiotic theory provides a lens to interpret these children's book-related interactions as evidence of emergent comprehension. In general, the children were gradually more attentive to function, topical content, image, and print, eventually showing the ability to merge multimodal signs to create textual meaning. (Contains 2 tables.)