Anonymous is a decentralized international activist and hacktivist collective and movement primarily known for its various cyberattacks against several governments, government institutions and government agencies, corporations, and the Church of Scientology.

Anonymous originated in 2003 on the imageboard 4chan representing the concept of many online and offline community users simultaneously existing as an "anarchic", digitized "global brain" or "hivemind". Anonymous members (known as anons) can sometimes be distinguished in public by the wearing of Guy Fawkes masks in the style portrayed in the graphic novel and film V for Vendetta. Some anons also opt to mask their voices through voice changers or text-to-speech programs.

Dozens of people have been arrested for involvement in Anonymous cyberattacks in countries including the United States, the United Kingdom, Australia, the Netherlands, South Africa, Spain, India, and Turkey. Evaluations of the group's actions and effectiveness vary widely. Supporters have called the group "freedom fighters" and digital Robin Hoods, while critics have described them as "a cyber lynch-mob" or "cyber terrorists". In 2012, Time called Anonymous one of the "100 most influential people" in the world. Anonymous' media profile diminished by 2018, but the group re-emerged in 2020 to support the George Floyd protests and other causes.

The philosophy of Anonymous offers insight into a long-standing political question that has gone unanswered with often tragic consequences for social movements: what does a new form of collective politics look like that wishes to go beyond the identity of the individual subject in late capitalism?

Internal dissent is also a regular feature of the group. A website associated with the group describes it as "an Internet gathering" with "a very loose and decentralized command structure that operates on ideas rather than directives". Gabriella Coleman writes of the group: "In some ways, it may be impossible to gauge the intent and motive of thousands of participants, many of who don't even bother to leave a trace of their thoughts, motivations, and reactions. Among those that do, opinions vary considerably."

Broadly speaking, Anons oppose Internet censorship and control and the majority of their actions target governments, organizations, and corporations that they accuse of censorship. Anons were early supporters of the global Occupy movement and the Arab Spring. Since 2008, a frequent subject of disagreement within Anonymous is whether members should focus on pranking and entertainment or more serious (and, in some cases, political) activism.

We [Anonymous] just happen to be a group of people on the Internet who need—just kind of an outlet to do as we wish, that we wouldn't be able to do in regular society. ...That's more or less the point of it. Do as you wish. ... There's a common phrase: 'we are doing it for the lulz.'

— Trent Peacock, Search Engine: The Face of Anonymous, February 7, 2008.