Complexity in product development (PD) projects can emanate from the product design, the development process, the development organization, the tools and technologies applied, the requirements to be met, and other domains.  In each of these domains, complexity arises from the numerous elements and their multitude of relationships, such as between the components of the product being developed, between the activities to develop them, and among the people doing the activities. One approach to handing this complexity is to represent and analyze these domains’ design structures or architectures.  The Design Structure Matrix (DSM) has proved to be a very helpful tool for representing and analyzing the architecture of an individual system such as a product, process, or organization. Like many tools, the DSM has been applied in a variety of areas outside its original domain, as researchers and practitioners have sought to leverage its advantages.  Along the way, however, its fundamental rules (such as being a square matrix) have been challenged.  In this paper we formalize an approach to using a Domain Mapping Matrix (DMM) to compare two DSMs of different project domains.  A DMM is a rectangular (m x n) matrix relating two DSMs, where m is the size of DSM₁ and n is the size of DSM₂.  DMM analysis augments traditional DSM analyses. Our comparison of DSM and DMM approaches shows that DMM analysis offers several benefits.  For example, it can help (1) capture the dynamics of PD, (2) show traceability of constraints across domains, (3) provide transparency between domains, (4) synchronize decisions across domains, (5) cross-verify domain models, (6) integrate a domain with the rest of a project or program, and (7) improve decision making among engineers and managers by providing a basis for communication and learning across domains.