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.

According to Dahl, “A has power over B to the extent that he can get B to do something that B would not otherwise do.” Dahl gave as an example a professor threatening a student with a failing grade if he did not read a certain book during the holidays.

He proposes that in a democracy, the masses and the leaders govern together. Who Governs? is an influential contribution to scholarship on the concept of power. Dahl conceptualizes power as the ability of A to make B do something that the latter would not otherwise do.

In political science, the term polyarchy (poly "many", arkhe "rule") was used by Robert A. Dahl to describe a form of government in which power is invested in multiple people. It takes the form of neither a dictatorship nor a democracy.