Purpose: Many well-accepted systems for determining difficulty level exist for books children read independently, but few are available for determining the wide range of difficulty levels of storybooks read aloud to preschoolers. Also, the available tools list book characteristics only on the basis of parents' or authors' opinions. We created an empirically derived difficulty-level system on the basis of 22 speech-language pathologists' (SLPs) judgments of specific storybooks used in preschooler read-alouds. Method: SLPs sorted 11 storybooks into ranked stacks on the basis of how difficult they thought the storybooks would be for preschoolers to understand when read aloud. SLPs described each stack globally as well as why they assigned each storybook to a particular stack. From transcriptions of the explanations, we derived a glossary of book characteristics using content analysis. We created a difficulty-level scale using a multivariate analysis technique that simultaneously analyzed book sorts and glossary terms. Results: The book selection system includes a glossary of book characteristics, a 4-level difficulty scale, and exemplar books for each level. Conclusion: This empirically derived difficulty-level system created for storybooks read aloud to preschoolers represents a step toward filling a gap in the read-aloud literature.