The Waldensians, founded in 1177 by Peter Waldo, are a Christian church. They rejected the traditions of the Roman Catholic Church, instead choosing to follow the Bible alone. Thus they can be seen as a form of proto-Protestantism. The Catholic church declared their views heretical and began to persecute them; many Waldensians were martyred and many others had to flee to remote places (such as the Alps) to escape persecution.
They are widely admired by Protestants as forerunners of the Reformation, even by those Protestant groups that do not directly descend from them. When the Protestant Reformation came in the 1500s, many of the Waldensians joined. The bulk of them adopted Calvinism. There is still a Waldensian movement surviving in Italy to this day. In 1975 it merged with the Methodist Church, creating a new body that today holds membership in the World Council of Churches and several international Methodist federations.
See also The Waldensian Confession of Faith which they adopted.