Blasphemy is a speech crime and religious crime usually defined as an utterance that shows contempt, disrespects or insults a deity, an object considered sacred or something considered inviolable. Some religions regard blasphemy as a religious crime, especially the Abrahamic religions, including insulting the prophet Muhammad in Islam, speaking the "sacred name" in Judaism, and the "eternal sin" in Christianity.

In the early history of the Church heresy received more attention than blasphemy because it was considered a more serious threat to Orthodoxy. Blasphemy was often regarded as an isolated offense wherein the faithful lapsed momentarily from the expected standard of conduct. When iconoclasm and the fundamental understanding of the sacred became more contentious matters during the Reformation, blasphemy was treated similar to heresy, and accusations of blasphemy were made not only against people who made off-the-cuff profane remarks while drunk, but against those types of persons who espoused unorthodox ideas that religious officials considered dangerous.

Blasphemy laws were abolished in England and Wales in 2008, and in Ireland in 2020. Scotland repealed its blasphemy laws in 2021. Many other countries have abolished blasphemy laws including Denmark, the Netherlands, Iceland, Norway and New Zealand. As of 2019, 40 percent of the world's countries still had blasphemy laws on the books, including 18 countries in the Middle East and North Africa, or 90% of countries in that region. Dharmic religions, such as Hinduism, Buddhism and Jainism, have no concept of blasphemy and hence prescribe no punishment.