The government of the parliamentary party during the Puritan Revolution of 1640–60 instituted changes in judicial and legal procedures to maintain its power and subdue its enemies. This study of treason trials conducted by the state will examine their legal basis and the events and activities considered treasonable. It will show the ways in which the concept of treason changed under a revolutionary government, and to what extent those trials conducted during the interregnum differed in their legal—judicial bases and content from those held before the King's death. Although there were hundreds of treason convictions during the interregnum throughout England, either by military courts-martial, or by common-law courts sitting in the provinces — as is shown by the Acts providing for die sale of estates forfeited to the Commonwealth for treason — this discussion will limit itself to trials initiated by the government in London. These state trials illustrate die political use of the treason charge; diey provide a direct link between the enactment of the interregnum treason laws and their implementation by the same legislative body. Not only was the meaning of treason determined, and die machinery of trial set up, by parliament; but who was to be tried was also decided eidier by parliament or die Council of State, and, after 1654, by the Protector and his council. It will dierefore be instructive to examine the types of treasonous action considered sufficiendy threatening to warrant parliamentary attention.