Open Source Architecture is a visionary manifesto for the architecture of tomorrow that argues for a paradigm shift from architecture as a means of supporting the ego-fueled grand visions of “starchitects” to a collaborative, inclusive, network-driven process inspired by twenty-first-century trends such as crowd-sourcing, open access, and mass customization. The question is how collaborative design can avoid becoming design-by-committee. Authors Carlo Ratti and Matthew Claudel navigate this topic nimbly in chapters such as “Why It Did Not Work” and “Learning from the Network.” They also meet the essential requirement of any manifesto, considering the applications of open-source architecture not only conceptually but also in practice, in chapters such as “Open Source Gets Physical” and “Building Harmonies.” Open Source Architecture is an important new work on the frontlines of architectural thought and practice.