High treason is criminal disloyalty to one's monarch or country. Participating in a war against one's country, attempting to overthrow its government, spying on its military, its diplomats, or its secret services for a hostile and foreign power, or attempting to kill its head of state are perhaps the best-known examples of high treason. High treason requires that the alleged traitor has obligations of loyalty in the state he or she betrayed, such as citizenship, although presence in the state at the time is sufficient. High treason is considered a serious offense, and carries the death penalty in some countries.
Historically, in common law countries high treason was differentiated from petty treason, which was the act of killing a lawful superior (such as a servant killing his or her master or mistress). It was, in effect, considered a more serious degree of murder. As jurisdictions around the world abolished petty treason, the concept of petty treason gradually faded, and today use of the word "treason" generally refers to "high treason."