He established the pluralist theory of democracy—in which political outcomes are enacted through competitive, if unequal, interest groups—and introduced "polyarchy" as a descriptor of actual democratic governance.

An originator of "empirical theory" and known for advancing behavioralist characterizations of political power, Dahl's research focused on the nature of decision making in actual institutions, such as American cities.

[1][2] He is the most important scholar associated with the pluralist approach to describing and understanding both city and national power structures.

[4] This long-term contact with local people became decisively important for his political attitudes and research interests.

He served in Europe during World War II, was the leader of a small reconnaissance platoon in an infantry regiment, and earned a Bronze Star.

[7] After World War II, Dahl returned to Yale in 1946, where he was offered a temporary position teaching American government.

[16][12] In the late 1950s and early 1960s, he was involved in an academic disagreement with C. Wright Mills over the nature of politics in the United States.

(1961), he examines the power structures (both formal and informal) in the city of New Haven, Connecticut, as a case study, and finds that it supports this view.

[17] From the late 1960s onwards, his conclusions were challenged by scholars such as G. William Domhoff and Charles E. Lindblom (a friend and colleague of Dahl).