In the context of platforms, an open architecture is instrumental in enabling innovation by complementors. But as complementors increasingly deplete the innovation opportunities that the platform architecture affords, the platform architecture must evolve to reinvigorate the platform’s generative capacity. This article underscores the role of complementors in the process of platform architecture evolution by introducing the notion of architectural generativity. Architectural generativity involves actively soliciting and selectively incorporating contributions from complementors to help evolve the platform in unforeseen ways. In the case of the Mozilla Firefox web browser platform, complementors contributed new ways to facilitate access to the platform’s technological components and suggested better ways to control the platform and its architecture.