In an era of rapid change, uncertainty, and hyperpartisanship, when wicked problems abound, tools for solving public problems are more essential than ever. The authors lay out a new theory for collaborative practice in planning, public administration, and public policy. Planning with Complexity provides both theoretical underpinnings and extensive case material on collaboration and offers ways of understanding and conducting effective practice. Collaborative rationality means collaboration that is inclusive, informed, grounded in authentic dialogue, and that results in wise and durable outcomes. The scholar-practitioner author team builds on more than 40 years of research, teaching, and practice addressing environmental issues, housing, and transportation. This second edition updates the case studies and adds new examples reflecting the global spread of collaborative practices. It builds on insights that have recently emerged in the literature. More than 75 new references have been incorporated, along with new tables. This book is essential for students, educators, scholars, and reflective practitioners in public policy fields in the 21st century.