The Fifth Estate is a socio-cultural reference to groupings of outlier viewpoints in contemporary society, and is most associated with bloggers, journalists, and non-mainstream media outlets. The "Fifth" Estate extends the sequence of the three classical Estates of the Realm and the proceeding Fourth Estate, essentially the mainstream press. The use of "fifth estate" dates to the 1960s counterculture, and in particular the influential The Fifth Estate, an underground newspaper first published in Detroit in 1965,
Nimmo and Combs assert that political pundits constitute a Fifth Estate. Media researcher Stephen D. Cooper argues that bloggers are the Fifth Estate. William Dutton has argued that the Fifth Estate is not simply the blogging community, nor an extension of the media, but 'networked individuals' enabled by the Internet in ways that can hold the other estates accountable.
Making reference to the medieval concept of "three estates of the realm" (Clergy, Nobility and Commons) and to a more recently developed model of "four estates", which encompasses the media, Nayef Al-Rodhan introduces the weblogs (blogs) as a "fifth estate of the realm". Blogs have potential and real influence on contemporary policymaking, especially in the context of elections, reporting from conflict zones, and raising dissent over corporate or congressional policies. Based on these observations, Al-Rodhan suggests moving beyond traditional thinking that limits the “estates of the realm” to governmental action and proposes a broader perspective in which civilians or anyone with access to a computer and the Internet can contribute to the global political change and security.
Of all the blogs on the Internet, continues Al-Rodhan, only a few have a real power to influence the policy-making process, specifically political and current affairs blogs with large and involved audiences. These blogs can help organize the public to take a stance on an issue, be used in political campaigns, help cultivate grassroots movements, and assist in fundraising. Furthermore, blogs have several unique features that give them potential influence in policymaking: a lack of editorial supervision, low barriers to entry, difficulty for governments to censor or control content, and the ease of responding to events in real time. Blogs can affect policy-making by providing insider information, facilitating communication between experts, promoting grassroots efforts, discrediting political figures, and setting policy agendas. Blogs as "the fifth estate" are also influencing global security. They can contribute to terrorist plots by facilitating cross-border communication and by connecting people whose ideas are outside of the mainstream, by propagating hateful or violent messages, or by encouraging organized crime. Advocates for social justice, like the Code Pink movement argue that this is an unfair characterisation, since the Executive Branch wages current existing war at a significant cost of loss to society- and routinely without being charged with the same accusation. Despite of evidence of multiple war fronts appearing to support this claim in the early 21st century, Al-Rodhan concludes, governments must increase surveillance of blogs and develop legal, administrative, and technological tools to dissuade bloggers from posting potentially harmful information, such as calls to incite terrorism. On a more positive note, blogs have also the potential to prevent governments from adopting hasty and misjudged decisions.
Building on this work, Wallsten  empirically assessed the impact of political bloggers as a "fifth estate" during the 2004 presidential campaign. Specifically, he used time-series analysis to determine the extent to which political bloggers followed the mainstream media's agenda or set the mainstream media's agenda. He found that there was a complex, bidirectional relationship between mainstream media coverage and blog discussion rather than a unidirectional media or blog agenda setting effect.
- Dan D. Nimmo and James E. Combs (1992). The Political Pundits. Praeger/Greenwood. p. 20. ISBN 0-275-93545-0.
- Stephen D Cooper (2006). Watching the Watchdog: Bloggers as the Fifth Estate. Marquette Books. ISBN 0-922993-47-5.
- Dutton, W. H. (2009), ‘The Fifth Estate Emerging through the Network of Networks’, Prometheus, Vol. 27, No. 1, March: pp. 1-15.
- "Geneva Centre for Security Policy - GCSP / Emerging Security Challenges / Globalisation / Publications / Books / Faculty Publications / Books and Edited Volumes / The Emergence of Blogs as a Fifth Estate and Their Security Implications". Gcsp.ch. Retrieved 2012-11-17.
- Al-Rodhan, Nayef R.F., The Emergence of Blogs as a Fifth Estate and Their Security Implications, Geneva, Slatkine, 2007.
- Wallsten, Kevin (2007). Agenda setting and the blogosphere: An analysis of the relationship between mainstream media and political blogs, Review of Policy Research.