Modularity is a design property of the architecture of products, organizations, and interfirm networks; modularization is a process that affects those designs while also shaping firm boundaries and industry landscapes; and ‘modularity’ is a cognitive frame that guides categorization and interpretation of a wide array of economic phenomena. Modularity-as-property and modularization-as-process are deeply intertwined; while modularization processes are ubiquitous and perpetual as engineers and managers seek to understand interdependencies across the boundaries of product and organizational architecture, the extent to which modularity-as-property is achieved must be assessed empirically. The framing of ‘modularity’ affects strategy by prompting a particular dynamic—and directionality—in the interplay between modularity-as-property and modularization-as-process. I analyze product architecture initiatives in the global automotive industry, examining first the industry-level antecedents of the emergent production-based definition of modules and then two firm-level modularity initiatives that both were based on this common definition, but framed their strategies differently. In the first case, a ‘modularity’ frame based on a computer industry analogy resulted in overemphasis on achieving modularity-as-property that created barriers to learning about cross-module interdependencies. In the second case, early emphasis on modularization-as-process yielded quasi-integrated organizational arrangements that facilitated long-term design improvements. Overall, this single-industry case study demonstrates the importance of examining the context-specific antecedents of module definition; the multiplicity of potential barriers to modularity that can lead to persistent integrality; the need for longitudinal inquiry into the ‘mirroring’ hypothesis that pays as much attention to process as to property; and the power of modularity as a cognitive frame, which helps explain divergent findings in modularity research.