Excommunication or disfellowshiping is an institutional act of religious censure used to end or at least regulate the communion of a member of a congregation with other members of the religious institution who are in normal communion with each other. The purpose of the institutional act is to deprive, suspend, or limit membership in a religious community or to restrict certain rights within it, in particular, those of being in communion with other members of the congregation, and of receiving the sacraments.

It is practiced by all of the ancient churches (such as the Catholic Church, Oriental Orthodox churches and the Eastern Orthodox churches) as well as by other Christian denominations, but it is also used more generally to refer to similar types of institutional religious exclusionary practices and shunning among other religious groups. The Amish have also been known to excommunicate members that were either seen or known for breaking rules, or questioning the church, a practice known as shunning. Jehovah's Witnesses use the term disfellowship to refer to their form of excommunication.

The word excommunication means putting a specific individual or group out of communion. In some denominations, excommunication includes spiritual condemnation of the member or group. Excommunication may involve banishment, shunning, and shaming, depending on the group, the offense that caused excommunication, or the rules or norms of the religious community. The grave act is often revoked in response to manifest repentance.