A dissident, broadly defined, is a person who actively challenges an established doctrine, policy, or institution. When dissidents unite for a common cause they often affect a dissident movement.
Eastern bloc dissidents
The term dissident was used in the Eastern bloc, particularly in the Soviet Union, in the period following Joseph Stalin's death until the fall of communism. It was attached to citizens who criticized the practices or the authority of the Communist Party. The people who used to write and distribute non-censored, non-conformist samizdat literature were criticized in the official newspapers. Soon, many of those who were dissatisfied with the Soviet Bloc began to self-identify as dissidents. This radically changed the meaning of the term: instead of being used in reference to an individual who opposes society, it came to refer to an individual whose non-conformism was perceived to be for the good of a society. An important element of dissident activity in "Soviet Russia" was informing society (both inside the Soviet Union and in foreign countries) about violation of laws and human rights: see Chronicle of Current Events (samizdat) and Moscow Helsinki Group. Some famous Soviet dissents were Aleksandr Solzhenitsyn and Andrei Sakharov.
Republican dissidents in Ireland
The term dissident has become the primary term to describe Irish republicans who politically continue to oppose Good Friday Agreement of 1998 and reject the outcome of the referendums on it. These political parties also have paramilitary wings which espouse violent methods to achieve a United Ireland.
Irish republican dissident groups include the Irish Republican Socialist Party (founded in 1974 – its currently-inactive paramilitary wing is the Irish National Liberation Army), Republican Sinn Féin (founded in 1986 – its paramilitary wing is the Continuity IRA), and the 32 County Sovereignty Movement (founded in 1997 – its paramilitary wing is the Real IRA). In 2006 the Óglaigh na hÉireann emerged, which is a splinter group of the Continuity IRA.
The term "dissident" has been applied to people in the United States to denote people who have exposed US government secrets, as in the example of Chelsea Manning who revealed the videos of Baghdad airstrikes and other information to the world through Wikileaks, or Edward Snowden who exposed the US government spying on the internet activity of people and government officials of other countries, including allied countries, as well as its own citizens, such as in the case of the PRISM and XKeyScore programs. 
- List of Chinese dissidents
- List of Singaporean dissidents
- Cuban dissident movement
- Political dissent
- Tor (anonymity network)
- Harper, Douglas. "dissident". Online Etymology Dictionary. Retrieved 2009-03-29.
- Chronicle of Current Events (samizdat) (Russian)
- Universal Declaration of Human Rights General Assembly resolution 217 A (III), United Nations, 10 December 1948
- Proclamation of Tehran, Final Act of the International Conference on Human Rights, Teheran, 22 April to 13 May 1968, U.N. Doc. A/CONF. 32/41 at 3 (1968), United Nations, May 1968
- CONFERENCE ON SECURITY AND CO-OPERATION IN EUROPE FINAL ACT. Helsinki, 1 aug. 1975
- "Who are the dissidents?". BBC News. 2009-03-10. Retrieved 2009-10-13.
- Assange, Manning, Snowden are new dissidents
- Press article on Snowden
- NSA taps all you do online
|Look up dissident in Wiktionary, the free dictionary.|