Thirty years ago, Alan Altshuler, in a devastating critique that has never been effectively answered, challenged the legitimacy of comprehensive planning and of planners' expertise. He called on the field to reinforce its theoretical arsenal. This article takes up his challenge, contending that not only have practices now arisen that make comprehensive planning possible, but also political and social theory has evolved to provide its intellectual grounding. The article argues that consensus building with stakeholders offers a model for planning that responds to each of Altshuler's critiques. Consensus building is shown to be founded on assumptions about the nature of knowledge, about the organization of interests, and about the nature of the public interest that differ from those Altshuler applied. Evidence is taken from eight in-depth case studies of consensus building over growth and environmental issues in California, and from a study of the New Jersey state planning process. The article concludes with a discussion of how consensus building may be used for local comprehensive planning.