In ancient Roman law this was a negative command by the praetor forbidding certain actions. In the Roman Catholic Church it is a command which prohibits or denies to the faithful participation in certain sacred acts, even though they remain in communion with the church. An interdict may be directed toward two purposes: its general use is a censure to bring about a desired cessation of an act or condition, but it may also be used as a vindicative penalty to bring about atonement for an offense.

There are several types of interdict. A personal interdict affects the person against whom it is directed wherever he goes, while a local interdict is concerned only with a certain locality and does not affect any who leave the area. In a particular personal interdict, the recipient or recipients of the ban are explicitly named; but in a general personal interdict, all those in a certain group are affected. A particular local interdict is directed against one sacred place, and a general local interdict affects a larger area, such as a diocese, province, state, or nation. A bishop may impose an interdict on a particular parish or the people of a parish, but only the Apostolic See may impose interdicts affecting larger areas or groups. The sacred acts which are prohibited by an interdict include the celebration of the Mass, Benediction of the Blessed Sacrament, and burial rites. Exceptions to the prohibitions of the interdict are granted to the dying and on some of the greater feasts (e.g., Christmas and Easter).

Although the interdict was used in the early church in the sixth century, it was not part of ecclesiastical law until the eleventh, and was not completely institutionalized until later. It was a frequent weapon of the medieval papacy in dealing with obstinate monarchs, as in the case of Innocent III's* interdict on England when King John (1199-1216) refused to allow the papal appointee (Stephen Langton) to the archbishopric of Canterbury entry into the country. Theoretically the interdict is still applicable, but is no longer held to be an active instrument of the Roman Catholic Church.