In law, coming into force or entry into force (also called commencement) is the process by which legislation, regulations, treaties and other legal instruments come to have legal force and effect. The term is closely related to the date of this transition. The point at which such instrument comes into effect may be set out in the instrument itself, or after the lapse of a certain period, or upon the happening of a certain event, such as a proclamation or an objective event, such as the birth, marriage, reaching a particular age or death of a certain person. On rare occasions, the effective date of a law may be backdated to a date before the enactment.

To come into force, a treaty or Act first needs to receive the required number of votes or ratifications. Although it is common practice to stipulate this number as a requirement in the body of the treaty itself, it can also be set out in a superior law or legal framework, such as a constitution or the standing orders of the legislature in which it originated.

Coming into force generally includes publication in an official gazette so that people know the law or treaty exists.