Munificentissimus Deus ( The most bountiful God) is the name of an apostolic constitution written by Pope Pius XII. It defines ex cathedra the dogma of the Assumption of the Blessed Virgin Mary. It was the first ex-cathedra infallible statement since the official ruling on papal infallibility was made at the First Vatican Council (1869–1870). In 1854 Pope Pius IX made an infallible statement with Ineffabilis Deus on the Immaculate Conception of the Virgin Mary, which was a basis for this dogma. The decree was promulgated on 1 November 1950.