Apostacy is generally held to be the abandonment or renunciation of a religion or its core beliefs. However, the actions that may cause someone to be accused of apostacy have differed both over time and from one religion to another.
Christianity
Apostacy is pictured in the Christian bible as a rejection of God or a turning away from God. The Roman Catholic Church also used the word ‘apostacy’ to refer to Chistian monks who renounced their monastic vows and to members of the clergy who abandoned their clerical occupation. Moreover, the medieval church in Europe often did not distinguish clearly between apostasy and heresy – having a belief inconsistent with official church doctrine. Both were sometimes punished by death.
Islam
Someone is considered an apostate if they convert from Islam to another religion, deny one or more of the main tenets of Islam, treat a copy of the Quran disrespectfully or refer disrespectfully to one of Islam’s prophets.
Muslims generally believe that apostacy is a crime against God for which God has fixed the penalties. These include the annulment of the apostate’s marriage, the seizure of their children and confiscation of their property, and execution. The laws of some Muslim countries – including Iran, Saudi Arabia and Mauretania – state clearly that apostacy is a capital crime though executions are rare.