Platforms – architectures of related standards that allow modular substitution of complementary assets – feature prominently in technology-intensive industries. The motivations for firms to adopt a particular platform strategy and the ways in which platform strategies change over time are not fully understood. This thesis examines the platform strategies of three leading vendors in the Electronic Design Automation (EDA) industry from 1987 to 2002. It employs a two-part research design: (i) pattern-matching to operationalize and test a three-stage explanation previously developed by West
(2003) to account for the evolution of platform strategies by firms in the computer industry, followed by (ii) explanation-building to account for differences between observations and the expected pattern. The pioneering EDA firm matches the expected pattern, but two other firms bypass stage one to enter at stage two with open standards. All three firms later move to stage three simultaneously by adopting hybrid open source strategies.