The Reformation began in the early 16th century when Martin Luther posted 95 theses criticizing the practices of the Catholic Church. Instead of merely reforming the Church, as had been done on several occasions throughout the Middle Ages, this new protest resulted in a permanent break and the creation of Protestant Christian sects.
About Guide to European History Robert Wilde provides a clear, concise, and informative introduction to what the Reformation was, how it came about, the changes made in Protestant churches, the course the Reformation took and its aftermath.
A Protestant is one who follows Protestantism, the form of Christianity created during the Reformation. Rob Wilde explains how the word came to be used.
A quick review of Bard Thompson's Humanists and Reformers: A History of the Renaissance and Reformation.
Anabaptists were various Protestant sects that denied the validity of infant baptism. A four-page article from the 1911 Encyclopedia.
The Confession of Basel was one of the many statements of faith produced by the Reformation. A concise article from the 1911 Encyclopedia.
Extensive article by J. P. Kirsch explores the events from a Catholic perspective.