Blasphemy is defamation of God or gods. Many cultures disapprove of speech or writing which defames the God or gods of their established religions, and these restrictions have the force of law in some countries.

The public domain 1913 Webster's Unabridged Dictionary defines blasphemy as:

Blasphemy (Blas"phe*my) n. [L. blasphemia, Gr. : cf. OF. blasphemie.]

• An indignity offered to God in words, writing, or signs; impiously irreverent words or signs addressed to, or used in reference to, God; speaking evil of God; also, the act of claiming the attributes or prerogatives of deity. When used generally in statutes or at common law, blasphemy is the use of irreverent words or signs in reference to the Supreme Being in such a way as to produce scandal or provoke violence.

Figuratively, of things held in high honor: Calumny; abuse; vilification.

There has been a recent tendency in Western countries towards the repeal or reform of blasphemy laws, and these laws are only infrequently enforced where they exist. Such laws still exist in several countries, such as Spain (Article 525 of the criminal code), Germany (Article 166 of the criminal code), and Italy. In the United States, the First Amendment guarantees a relatively unlimited right of free speech, although some US states still have blasphemy laws on the books. Chapter 272 of Massachusetts' criminal code states, for example:

Section 36. Whoever wilfully blasphemes the holy name of God by denying, cursing or contumeliously reproaching God, his creation, government or final judging of the world, or by cursing or contumeliously reproaching Jesus Christ or the Holy Ghost, or by cursing or contumeliously reproaching or exposing to contempt and ridicule, the holy word of God contained in the holy scriptures shall be punished by imprisonment in jail for not more than one year or by a fine of not more than three hundred dollars, and may also be bound to good behavior.