Citizen journalism (also known as "public", "participatory", "democratic" or "street journalism") is the concept of members of the public "playing an active role in the process of collecting, reporting, analyzing and disseminating news and information," according to the seminal 2003 report We Media: How Audiences are Shaping the Future of News and Information. Authors Bowman and Willis say: "The intent of this participation is to provide independent, reliable, accurate, wide-ranging and relevant information that a democracy requires."

Citizen journalism should not be confused with community journalism or civic journalism, which are practiced by professional journalists, or collaborative journalism, which is practiced by professional and non-professional journalists working together. Citizen journalism is a specific form of citizen media as well as user generated content.

Mark Glaser, a freelance journalist who frequently writes on new media issues, said in 2006:

The idea behind citizen journalism is that people without professional journalism training can use the tools of modern technology and the global distribution of the Internet to create, augment or fact-check media on their own or in collaboration with others. For example, you might write about a city council meeting on your blog or in an online forum. Or you could fact-check a newspaper article from the mainstream media and point out factual errors or bias on your blog. Or you might snap a digital photo of a newsworthy event happening in your town and post it online. Or you might videotape a similar event and post it on a site such as YouTube.

In What is Participatory Journalism?, J. D. Lasica classifies media for citizen journalism into the following types:

1. Audience participation (such as user comments attached to news stories, personal blogs, photos or video footage captured from personal mobile cameras, or local news written by residents of a community)
2. Independent news and information Websites (Consumer Reports, the Drudge Report)
3. Full-fledged participatory news sites (NowPublic, OhmyNews, DigitalJournal.com, GroundReport)
4. Collaborative and contributory media sites (Slashdot, Kuro5hin, Newsvine)
5. Other kinds of "thin media." (mailing lists, email newsletters)
6. Personal broadcasting sites (video broadcast sites such as KenRadio).

New media theorist Terry Flew states that there are 3 elements "critical to the rise of citizen journalism and citizen media": open publishing, collaborative editing and distributed content. From this perspective, Wikipedia itself is the largest and most successful citizen journalism project, with news often breaking through Wikipedia editors, and stories being maintained as new facts emerge.