The Council of Trent was the 19th Ecumenical Council of the Roman Catholic Church. It opened on Dec. 13, 1545 and closed on Dec. 4, 1563 and was held in Trent, in Northern Italy. The Council was a response to the Reformation which was then heavily underway. The Council condemned the Reformation's doctrine of justification by faith alone and also reestablished various practices within the Roman Catholic Church.
The Council of Trent was called by Pope Paul III who was pope from 1534 to 1549.
Related Article: Council of Trent: Canons on Justification.