McGann presents the largest and most comprehensive study of independent public policy research organizations in America conducted to date. The study is a comparative analysis of the history, evolving character, and strategy and structure of think tanks. In an attempt to capture the diversity that exits among these non-profit institutions, the study compares and contrasts seven categories of policy research organizations. The comparative analysis focuses on the 'target' audiences (markets), organizational structure, products, and staffing patterns of over 85 organizations. The study also examines why these institutions are so prevalent in the U.S., their role in the policy formulation process, and their relation to interest groups.