Antinomianism (Ancient Greek: ἀντί [anti] 'against' and νόμος [nomos] 'law') is any view which rejects laws or legalism and argues against moral, religious or social norms (Latin: mores), or is at least considered to do so. The term has both religious and secular meanings.

In some Christian belief systems, an antinomian is one who takes the principle of salvation by faith and divine grace to the point of asserting that the saved are not bound to follow the moral law contained in the Ten Commandments. Christian antinomians believe that faith alone guarantees humans' eternal security in Heaven regardless of one's actions.

The distinction between antinomian and other Christian takes on moral law is that antinomians believe that obedience to the law is motivated by an internal principle flowing from belief rather than from any external compulsion, devotion, or need. Antinomianism has been considered to teach that believers have a "license to sin" and that future sins do not require repentance. Johannes Agricola, to whom antinomianism was first attributed, stated "If you sin, be happy, it should have no consequence."

Examples of antinomians being confronted by the religious establishment include Martin Luther's critique of antinomianism, the Ranters of the English Civil War, and the Antinomian Controversy of the seventeenth-century Massachusetts Bay Colony. The charge of antinomianism has been levelled at Reformed, Baptist, and some nondenominational churches.

By extension, the word "antinomian" is also used to describe views in religions other than Christianity:

Antinomianism has been a point of doctrinal contention in the history of Christianity. At its root is an argument between salvation through faith alone and on the basis of good works or works of mercy.

The term antinomianism was coined by Martin Luther during the Reformation to criticize extreme interpretations of the new Lutheran soteriology. In the 18th century, John Wesley, the founder of the Methodist tradition, severely attacked antinomianism.

According to some Christian denominations, moral laws (as opposed to civil or ceremonial laws) are derivative of what St. Paul indirectly refers to as natural law (Rm 2.14–15). According to this point of view, the Mosaic law has authority only insofar as it reflects the commands of Christ and the natural law. Christian sects and theologians who believe that they are less constrained by laws than critics consider customary are often called "antinomian" by those critics. Thus, classic Methodist commentator Adam Clarke held, "The Gospel proclaims liberty from the ceremonial law, but binds you still faster under the moral law. To be freed from the ceremonial law is the Gospel liberty; to pretend freedom from the moral law is Antinomianism."