Unitatis Redintegratio is the Second Vatican Council's Decree on Ecumenism. It was passed by a vote of 2,137 to 11 of the bishops assembled and was promulgated by Pope Paul VI on November 21, 1964. The title in Latin means "Restoration of Unity" and is from the first line of the decree, as is customary with major Catholic documents (see incipit).
Read more about Unitatis Redintegratio: Contents, Policy On The Eastern Orthodox and Oriental Orthodox, Reformation Communities, Separated Brethren