Background:Concepts are defined generally as fundamental principles or global understandings specific to a field of expertise. Theories of situated cognition suggest that concepts may not have uniform meaning or representation in a particular social setting. Purpose/Hypothesis: The goal of this study was to investigate the process by which practicing engineers come to understand and use concepts in the context of their work. Design/Method: A researcher conducted ethnographic fieldwork at a private consulting engineering firm. Data sources included (a) field notes obtained via participant observation, (b) transcripts from interviews, and (c) artifacts collected on site. Results: Five emergent themes from the data are presented: (1) engineers identify constraints before they apply concepts, (2) engineers address project constraints by contextualizing abstract features of concepts, (3) engineers expand individual understanding of the concept by engaging in social negotiation of meaning, (4) concepts have multiple representations in engineering practice, and (5) engineers use material resources to efficiently address complex processes and problems associated with engineering concepts. These themes were analyzed using situative perspective to develop a model of conceptual growth in engineering practice. Conclusions: Findings suggest that student learning experiences should deliberately highlight the role of engineering concepts in the often ill-structured engineering problems present in authentic engineering work. Specific suggestions for incorporating the model into engineering education are offered as are directions for future research.