Collaborative rationality is even more important today than it was when this book was first published. We have moved into an era of divisiveness, hyperpartisanship, mutual blame, and incivility. Close elections like the British Brexit vote and the US vote for President Trump allow 51 percent of the public to impose its will on the other 49 percent regardless of the consequences. 1 We also live in a post-truth 2 world, where different sides have different “facts” and “fake news” can be indistinguishable from the real thing. It is a recipe for paralysis at best, disastrous policies at worst. Effective plans and policies can only be developed through thorough discussion among those who understand the situation and who depend on mutually trusted information. Collaborative rationality is about creating the conditions for such dialogue among stakeholders, experts, and the broader public. It draws on many forms of knowledge, from science and research, to practice of many kinds, and firsthand experience. When collaboration is done properly plans, proposals, and projects are more likely to be workable, implemented, and enjoy public support.