Scholars in science and technology studies (STS) have recently been called upon to advise governments on the design of procedures for public engagement. Any such instrumental function should be carried out consistently with STS’s interpretive and normative obligations as a social science discipline. This article illustrates how such threefold integration can be achieved by reviewing current US participatory politics against a 70-year backdrop of tacit constitutional developments in governing science and technology. Two broad cycles of constitutional adjustment are discerned: the first enlarging the scope of state action as well as public participation, with liberalized rules of access and sympathetic judicial review; the second cutting back on the role of the state, fostering the rise of an academic-industrial complex for technology transfer, and privatizing value debates through increasing delegation to professional ethicists. New rules for public engagement in the United Sates should take account of these historical developments and seek to counteract some of the anti-democratic tendencies observable in recent decades.