Policymakers and education scholars recommend incorporating mathematical modeling into mathematics education. Limited implementation of modeling instruction in schools, however, has constrained research on how students learn to model, leaving unresolved debates about whether modeling should be reified and explicitly taught as a competence, whether it should be taught holistically or atomistically, and whether students' limited domain knowledge is a barrier to modeling. This study used the theoretical lens of "legitimate peripheral participation" to explore how learning about modeling unfolds in a community of practice--civil engineering--known to develop modeling expertise among its members. Twenty participants were selected to represent various stages of engineering education, from first-year undergraduates to veteran practitioners. The data, comprising interviews, "think-aloud" problem-solving sessions, and observations of engineering courses, were analyzed to produce a description of how this professional community organizes learning about mathematical models and resolves general debates about modeling education.