WHAT HAVE SEVERAL DECADES OF HEALTH EDUCATION, PROMOTION, and engagement with community and academic partners taught us about community-based research in public health? We know that some lessons derive from specific studies,l,2 others from reviews of international research literature,3,and still others from guides that help practitioners apply their apparent lessons.5 This commentary blends the findings of these various studies, reviews, and guides with general principles and guidelines that have emerged from our combined experience and observations in academic, foundation, federal, state, and local situations in the United States, Canada, Australia, and other countries. Our comments center on community-based partnerships, coalitions, and infrastructure building, but we emphasize that horizontal community coalitions and partnerships must be based on strong vertical relationships between local entities and their state and national counterparts or headquarter organizations. We assume that university-based researchers are often, but not necessarily or always, part of community based partnership. In order to answer our first question, we pose additional questions: Why is some partnering essential to community-based research? How much partnering is needed to facilitate the research, community planning, and execution of programs? What are the principles and components of good community partnerships, and how do they fit with the principles of participatory research and the particular demands of academic-community partnerships? What are some cautions for partnerships that become large coalitions? Finally, what lessons have the large community trials in chronic disease prevention taught us?