The Reformation forced the Roman Catholic Church to define itself with new precision. The Council of Trent, meeting in sessions across nearly two decades, was that definition. It addressed Scripture and tradition, justification, the sacraments, and the authority of the Church.
Trent also reformed: it curbed the abuses — including the sale of indulgences — that had helped provoke the Reformation, and it reshaped the training of clergy and the conduct of bishops.
The council gave Roman Catholicism the doctrinal and disciplinary shape it would keep for four centuries, until the Second Vatican Council reopened many of the same questions in a new key. Trent's own decrees are described on the Roman Catholic tradition page.