Mystici corporis

Mystici corporis Christi (29 June 1943) is a papal encyclical issued by Pope Pius XII during World War II, on the Church as the Mystical Body of Christ. It is one of the more important encyclicals of Pope Pius XII, because of its topic, the Church, and because its Church concept was fully included in Lumen gentium but also strongly debated during and after Vatican II. The Church is called body, because it is a living entity; it is called the body of Christ, because Christ is its Head and Founder; it is called mystical body, because it is neither a purely physical nor a purely spiritual unity, but supernatural.

The encyclical followed the commencement of Nazi Germany's programs of "euthanasia" of the disabled, and race-based murders of Jews and other minorities, and is therefore significant for its reiteration of Church teachings against racism and the killings of people with disabilities.

The encyclical builds on a theological development in the 1920s and 1930s in Italy, France, Germany and England, which all re-discovered the ancient Pauline concept of the Mystical Body of Christ.Pius XII utilized these new discoveries and authoritatively added his directions to them, as the Dutch Jesuit Sebastian Tromp documented.Reginald Garrigou-Lagrange, Raimondo Spiazzi and Mariano Cordovani, all professors at the Pontificium Athenaeum Internationale Angelicum, the future Dominican Order-affiliated Pontifical University of Saint Thomas Aquinas, had a great influence on the drafting of the encyclical.

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