Sedition is a crime similar to treason but generally less serious. Views on sedition differs between countries, such as regarding certain criticisms of the government, which may be viewed as illegal sedition in some countries, but be protected by freedom of speech laws in others.
More specifically, conduct or language inciting rebellion against the authority of a government may be sedition, but Western countries have generally allowed, for example, Communists to argue for a Communist revolution, at least as a vague general idea, as long as there is not more specific incitement.
Sedition in its modern meaning first appeared in the Elizabethan Era (c. 1590) as the "notion of inciting by words or writings disaffection towards the state or constituted authority". "Sedition complements treason and martial law: while treason controls primarily the privileged, ecclesiastical opponents, priests, and Jesuits, as well as certain commoners; and martial law frightens commoners, sedition frightens intellectuals."
Australia's sedition laws were amended in anti-terrorism legislation passed on 6 December 2005, updating definitions and increasing penalties.
In late 2006, the Howard government proposed plans to amend Australia's Crimes Act 1914, introducing laws that mean artists and writers may be jailed for up to seven years if their work was considered seditious or inspired sedition either deliberately or accidentally. Opponents of these laws have suggested that they could be used against legitimate dissent.
Over the past year, Australian attorney-general Philip Ruddock has rejected calls by two reports — from a Senate committee and the Australian Law Reform Commission — to limit the sedition provisions in the Anti-Terrorism Act 2005 by requiring proof of intention to cause disaffection or violence. He has also brushed aside recommendations to curtail new clauses outlawing “urging conduct” that “assists” an “organisation or country engaged in armed hostilities” against the Australian military.
The new laws, inserted into the legislation last December, allow for the criminalization of basic expressions of political opposition, including supporting resistance to Australian military interventions, such as those in Afghanistan, Iraq and the Asia-Pacific region. 
During World War II former Mayor of Montreal Camillien Houde campaigned against conscription in Canada. On August 2, 1940, Houde publicly urged the men of Quebec to ignore the National Registration Act. Three days later, he was placed under arrest by the Royal Canadian Mounted Police on charges of sedition. After being found guilty, he was confined in internment camps in Petawawa, Ontario and Gagetown, New Brunswick until 1944. Upon his release on August 18, 1944, he was greeted by a cheering crowd of 50,000 Montrealers and won back his job as Montreal mayor in 1944's civic election. reference required
Sedition charges were not uncommon in New Zealand early in the twentieth century. For instance, Prime Minister Peter Fraser was convicted of sedition in his youth for arguing against conscription during World War I, and imprisoned for a year. Perhaps ironically, Fraser restored conscription as Prime Minister during World War II.
In New Zealand's first sedition trial in decades, Tim Selwyn was convicted of sedition (section 83 of the Crimes Act 1961) on 8 June 2006. Shortly after, in September 2006, the New Zealand Police laid a sedition charge against a Rotorua youth, Christopher Russell, 17, who was also charged with threatening to kill. The Police withdrew the sedition charge when Russell agreed to plead guilty on the other charge.
In March 2007, Mark Paul Deason, 32, manager of a tavern near the University of Otago, was charged with seditious intent although he was later granted police diversion when he pleaded guilty to publishing a document which encourages public disorder Deason ran a promotion for his Tavern that offered 1 litre of beer for 1 litre petrol. At the end of the promotion, the prize would have been a couch soaked in the petrol. It is presumed the intent was for the couch to be burned — a popular university student prank. Police also applied for Deason's liquor license to be revoked.
Following a recommendation from the New Zealand Law Commission, the New Zealand government announced on 7 May 2007 that the sedition law would be repealed. The Crimes (Repeal of Seditious Offences) Amendment Act 2007 was passed on 24 October 2007, and entered into force on 1 January 2008. 
The last prosecution for sedition in the UK was in 1972, when three people were charged with seditious conspiracy and uttering seditious words for attempting to recruit people to travel to Northern Ireland to fight in support of local Catholics. The seditious conspiracy charge was dropped, but the men received suspended sentences for uttering seditious words and for offences against the Public Order Act.
In 1977, a Law Commission working paper recommended that the common law offence of sedition in England and Wales be abolished. They said that they thought that this offence was redundant and that it was not necessary to have any offence of sedition. This proposal has not been implemented.
On 15 July 2008 Lord Bach, the Minister of Justice, announced the government's intention to repeal the offences of seditious and criminal libel.
There have been 24 attempts in the United States to regulate speech that has been deemed seditious. In 1798, President John Adams signed into law the Alien and Sedition Acts, the fourth of which, the Sedition Act or "An Act for the Punishment of Certain Crimes against the United States" set out punishments of up to two years' imprisonment for "opposing or resisting any law of the United States" or writing or publishing "false, scandalous, and malicious writing" about the President or Congress (but specifically not the Vice-President). The act was allowed to expire in 1801 after the election of Thomas Jefferson to the presidency. He was Vice President at the time of the Act's passage.
Under the Espionage Act of 1917, section 3 made it a crime, punishable by 20 years' imprisonment and a fine of up to $10,000, to wilfully spread false news of the US military with an intent to disrupt their operations, to foment mutiny in the ranks, or obstruct recruiting. The act was amended in 1918 by the Sedition Act, which expanded the purview of the Espionage Act to any statement criticizing the government. The act was upheld in 1919 in Schenck v. United States, but was largely repealed in 1921, leaving laws forbidding espionage and allowing military censorship of sensitive material.
In 1940, the Alien Registration Act or Smith Act was passed, which made it a crime to advocate or teach the desirability of overthrowing the United States Government, or to be a member of any organization which does the same. It was often used against Communist organizations. The act was invoked in three major trials, one of the Socialist Worker's Party in Minneapolis in 1941, resulting in 23 convictions, and again in 1944 in what became known as The Great Sedition Trial, of nationalist figures which ended in a mistrial. A series of trials of 140 leaders of the Communist Party USA was also predicated upon the Smith Act beginning in 1949, and lasting until 1957. Although the Supreme Court upheld the convictions of 11 CPUSA leaders in 1951, the court reversed itself in 1957 in Yates v. United States by ruling that teaching an ideal, no matter how harmful it may seem, does not equal advocating or planning its implementation. Although unused since at least 1961, the Smith Act remains US law.
Sedition is a punishable offence under the United States Uniform Code of Military Justice, Article 94.
- List of sedition trials in America
- Coup d'état
- Free speech
- Guerrilla warfare
- Resistance movement
- Sedition Act
- Seditious libel
- Lusk Committee
- Satire used to counter new sedition laws, ABC's Lateline transcript, 24 October 2006
- Australia’s new Sedition Laws, Mike Head, World Socialist Web Site, 27 October 2006
- Today in History: 22 December 1916 - Future PM Fraser charged with sedition, nzhistory.net.nz, History Group of the New Zealand Ministry for Culture and Heritage.
- Law advice body wants to scrap crime of sedition, New Zealand Herald, 17 October 2006
- Sedition by Example XXII: Christopher Russell, No Right Turn weblog, 28 February 2007
- Police move to cancel 'beer-for-petrol' publican's licence, Infonews.co.nz, 11 April 2007
- Diversion over petrol-soaked couch promo, Crime.co.nz, 29 March 2007
- Template:PDFlink, New Zealand Law Commission, 5 April 2007
- "Sedition law to be repealed". Radio New Zealand. 2007-05-07. http://www.radionz.co.nz/news/latest/200705071751/sedition_law_to_be_repealed. Retrieved 2007-05-05.
- "New Zealand repeals sedition law". Wikinews. 2007-10-24. http://en.wikinews.org/wiki/New_Zealand_repeals_sedition_law. Retrieved 2007-10-24.
- The Law Commission, Treason, Sedition and Allied Offences (Working Paper No.72), paragraph 47  EWLC C72, BAILII
- ‘Arcane’ laws of sedition and criminal libel scrapped. Times (2009-07-15). Retrieved on 2009-07-17.
- http://www.law.cornell.edu/uscode/10/usc_sec_10_00000894----000-.html Uniform Code of Military Justice