Provided is an integrated sketch of systematic changes in patterns of political participation and legitimation, and suggestions for where one might begin to look for the sources of such change. Following an introductory section, section 2 reviews time-series data on electoral participation, party identifications, and attitudes toward electoral institutions. Lines of explanation most often found in the research literature are outlined and evidence suggesting that such preferred explanations appear complete is reviewed. Section 3 sets the context for the argument by discussing the expanded activity and social penetration of the central government: the reorganization of the American political system (e.g., the reconfiguration of federalism) and the expansion of public authority and citizenship claims in the U.S. polity. Section 4 presents an explanatory sketch suggesting ways in which shifts in citizen repertories might be tied to institutions of the political environment. Evidence of expanding collective forms of political activity is presented in section 5. The final section discusses implications of the argument for understanding the character of "legitimation" in a changed polity. The report concludes that shifts in electoral participation, the changes in attitudes, and the increasing prominence of collective activity seem to constitute a reorganization of the U.S. political culture: an evolution from the associated politics of the "civic culture" to the claimant politics of a collective action polity. (LH)