The word interdict usually refers to an ecclesiastical penalty in the Roman Catholic Church. The most common usage is a penalty which suspends all public worship and withdraws the church's sacraments in a territory or country. An interdict issued against a country was to it the equivalent of issuance of excommunication against an individual. An interdict would cause all the churches to be closed, and almost all the sacraments not to be allowed (i.e. preventing marriage, confession, Anointing of the Sick, and the eucharist). It was used by the Pope during the Middle Ages as a way to influence rulers. For example, Pope Innocent III placed the kingdom of England under an interdict for seven years between 1208 and 1215 after King John refused to accept the pope's appointee as Archbishop of Canterbury.

An interdict can also be a penalty against a specific individual. It is like excommunication in that the person is barred from receiving the sacraments and participating in public worship, but it does not bar the person from continuing to hold and exercise ecclesistical office. Thus, for a lay member of the church, it is basically equivalent to excommunication.

Certain offenses incur an automatic interdict:

• Physical violence against a bishop
• Attempting to preside over or concelebrate in Mass while being a deacon or lay person
• Hearing and/or attempting to absolve confessions while being a deacon or lay person
• Falsely accusing a priest of soliciting adultery while in confession
• Attempting to marry while having a perpetual vow of chastity

The word interdict can also refer to a type of shield or military defense against attack.

May also refer to a court order prohibiting a certain course of action in some jurisdictions, eg. Scotland.