Treason is defined as an act of disloyalty against a nation or national sovereign by a citizen of that nation. It is usually treated very seriously by the penal system, as a single calculated act of treason can utterly destabilize an entire government. In most countries, conviction of high treason is accompanied with a death sentence, a long term of imprisonment, or a substantial fine. Someone who commits treason is called a traitor. Anyone can be a traitor, including ordinary citizens, members of the government, or active duty military.

The word for treason was first used in the English language in the 1200s, and appears to be related to a French word, traison, which means to hand over or surrender. A major act of treason would be an activity that is designed to lead directly to overthrow of a government, or carrying out a threat to a major state figure such as a member of the royal family or a President. If your nation is involved in a war, fighting on the side of the enemy is treason, and assisting enemy combatants is also treason. Spying and other acts of disloyalty are usually prosecuted under treason laws as well, as they are viewed as betrayals of trust which ultimately operate to undermine the government in power.

In the United States, treason is very narrowly defined, due to a European tradition of accusing political opponents of treason, which the Founders wanted to avoid. In other nations, treason may be less clearly spelled out in books of law, which can lead to unfair persecution. Far more people are prosecuted in America for sedition, an action or speech which is supposed to incite disloyalty, hatred, or treasonous behavior. Several Sedition Acts have been passed in the United States during war time, to allow the government to more easily punish agitators.

Sometimes the line between treason and politically legal activity can be very fine. For example, some critics believe that anti-war protesters are committing an act of treason by being unpatriotic. In other cases, individuals from within or outside a government may be advocating for radical changes which would completely reshape their nation. This could be viewed as treason by the party in power, as it would technically alter the status quo, although it not necessarily lead to collapse of the nation as a whole. Some political hardliners believe that their opponents are traitors, as demonstrated by the popular book Treason, by Ann Coulter, attacking the political views of the American left.