Blasphemy is speech or action treated as showing contempt for God, the sacred, or what a community holds inviolable. What has counted as blasphemy has varied enormously, and the category has almost always been entangled with public order and political authority as well as with religion, which is one reason its history is so hard to disentangle from the history of power.
In the Hebrew Bible, Leviticus 24:10-16 narrates the case of a man who "blasphemed the Name" and prescribes stoning. Rabbinic law then hedged the offence with requirements so strict, that the offender pronounce the Tetragrammaton itself, in the presence of witnesses who had warned him first, that conviction became practically unattainable, which is characteristic of the rabbis' handling of capital offences generally.
In the Christian tradition the Gospels present blasphemy as the charge on which Jesus was condemned (Mark 14:64), and speak of "blasphemy against the Holy Spirit" as the one sin not forgiven (Mark 3:29), a text that has caused considerable pastoral anxiety and that most theologians read as naming the settled refusal of forgiveness rather than any particular utterance. Christendom criminalised blasphemy widely; the English common law offences of blasphemy and blasphemous libel, which in practice protected only Christianity, survived until their abolition in England and Wales in 2008 and in Scotland in 2021.
In Islam, insulting God or the Prophet is a grave offence in classical law, though, as with apostasy, the Qur'an prescribes no fixed worldly penalty and the jurists derived one from other sources; the schools differ over whether repentance is accepted. Modern blasphemy legislation is the sharpest point of contemporary contention. Pakistan's provisions, chiefly sections 295-B and 295-C of its Penal Code as amended in the 1980s, carry a mandatory death sentence for defiling the name of the Prophet. No execution has been carried out under them, but accused persons have repeatedly been killed extrajudicially, and human rights organisations have documented extensive use of the law against religious minorities and in private disputes. International episodes, the 1989 fatwa against Salman Rushdie, the Danish cartoon controversy from 2005, and the murders at Charlie Hebdo in 2015, have kept the conflict between protection of religious sensibility and freedom of expression permanently in view.
The underlying disagreement is genuine and does not run neatly between religions. One position holds that religions and their founders should be protected from gratuitous insult, because the injury is real, because it falls on communities that are often already vulnerable, and because speech of this kind functions as harassment rather than argument. The other holds that criminalising blasphemy protects ideas rather than people, that such laws are invariably used by the powerful against the weak, and that they cannot be administered at all without a state deciding whose sacred counts. United Nations bodies moved away from the language of "defamation of religions" after 2011 toward a narrower focus on incitement to discrimination, hostility or violence, a shift that reflects the force of the second argument without dismissing the concern behind the first.