“The Overton window is the range of policies politically acceptable to the mainstream population at a given time. It is also known as the window of discourse. The term is named after Joseph P. Overton, who stated that an idea's political viability depends mainly on whether it falls within this range, rather than on politicians' individual preferences.

The Overton Window is an approach to identifying the ideas that define the spectrum of acceptability of governmental policies. Politicians can only act within the acceptable range. Shifting the Overton Window involves proponents of policies outside the window persuading the public to expand the window. Proponents of current policies, or similar ones within the window, seek to convince people that policies outside it should be deemed unacceptable.

In 1998, Noam Chomsky said:

"The smart way to keep people passive and obedient is to strictly limit the spectrum of acceptable opinion, but allow very lively debate within that spectrum—even encourage the more critical and dissident views. That gives people the sense that there's free thinking going on, while all the time the presuppositions of the system are being reinforced by the limits put on the range of the debate.”