Book excerpt: Leading theorists and practitioners trace the evolution of key ideas in urban and regional planning over the last hundred years Over the past hundred years of urbanization and suburbanization, four key themes have shaped urban and regional planning in both theory and practice: livability, territoriality, governance, and reflective professional practice. Planning Ideas That Matter charts the trajectories of these powerful planning ideas in an increasingly interconnected world. The contributors, leading theorists and practitioners, discuss livability in terms of such issues as urban density, land use, and the relationship between the built environment and natural systems; examine levels of territorial organization, drawing on literature on regionalism, metropolitanism, and territorial competition; describe the ways planning connects to policy making and implementation in a variety of political contexts; and consider how planners conceive of their work and learn from practice. Throughout, the emphasis is on how individuals and institutions—including government, business, professional organizations, and universities—have framed planning problems and ideas. The focus is less on techniques and programs than on the underlying concepts that have animated professional discourse over the years. The book is recommended for classroom use, as a reference for scholars and practitioners, and as a history of planning for those interested in the development of the field.