The public sphere (German: Öffentlichkeit) is an area in social life where individuals can come together to freely discuss and identify societal problems, and through that discussion influence political action. A "Public" is "of or concerning the people as a whole." Public Sphere is a place common to all, where ideas and information can be exchanged. Such a discussion is called public debate and is defined as the expression of views on matters that are of concern to the public—often, but not always, with opposing or diverging views being expressed by participants in the discussion. Public debate takes place mostly through the mass media, but also at meetings or through social media, academic publications and government policy documents. The term was originally coined by German philosopher Jürgen Habermas who defined the public sphere as "made up of private people gathered together as a public and articulating the needs of society with the state". Communication scholar Gerard A. Hauser defines it as "a discursive space in which individuals and groups associate to discuss matters of mutual interest and, where possible, to reach a common judgment about them". The public sphere can be seen as "a theater in modern societies in which political participation is enacted through the medium of talk" and "a realm of social life in which public opinion can be formed".

Describing the emergence of the public sphere in the 18th century, Habermas noted that the public realm, or sphere, originally was "coextensive with public authority", while "the private sphere comprised civil society in the narrower sense, that is to say, the realm of commodity exchange and of social labor". Whereas the "sphere of public authority" dealt with the state, or realm of the police, and the ruling class, or the feudal authorities (church, princes and nobility) the "authentic 'public sphere'", in a political sense, arose at that time from within the private realm, specifically, in connection with literary activities, the world of letters. This new public sphere spanned the public and the private realms, and "through the vehicle of public opinion it put the state in touch with the needs of society". "This area is conceptually distinct from the state: it [is] a site for the production and circulation of discourses that can in principle be critical of the state." The public sphere "is also distinct from the official economy; it is not an arena of market relations but rather one of the discursive relations, a theater for debating and deliberating rather than for buying and selling". These distinctions between "state apparatuses, economic markets, and democratic associations...are essential to democratic theory". The people themselves came to see the public sphere as a regulatory institution against the authority of the state. The study of the public sphere centers on the idea of participatory democracy, and how public opinion becomes political action.

The ideology of the public sphere theory is that the government's laws and policies should be steered by the public sphere and that the only legitimate governments are those that listen to the public sphere. "Democratic governance rests on the capacity of and opportunity for citizens to engage in enlightened debate". Much of the debate over the public sphere involves what is the basic theoretical structure of the public sphere, how information is deliberated in the public sphere, and what influence the public sphere has over society.