There are more than 500 million Protestants worldwide—they make up over 40 percent of Christians. All have their origins, some more directly than others, in the 16th-century Reformation begun by Martin Luther.
Several important figures and social changes set the stage for the Protestant Reformation. Some forerunners were influential: Pope Gregory VII, Erasmus, John Wycliffe, and John Hus. In addition, the cultural and intellectual movements of humanism and nominalism influenced the reformers, and created a large audience for them.
Almost every branch of Protestantism can be traced back to a few founders. Most of them build, at least to some degree, on the work of Luther, Zwingli, and Calvin.
The Bible is the scripture and thus the most important set of writings for Protestant churches. Protestants claim to place the Bible as the ultimate authority for belief and practice. In addition, some Protestant churches have creeds (formal statements of belief), while others are non-creedal.
Historical scholarship on Protestant churches often reflects the theological perspectives of the people writing the scholarship. Recently three trends have emerged in study of the 16th-century origins of Protestantism: a focus on the medieval nature of the Reformation, attention to the lives of all classes of people at the time of the Reformation, and a debate about the meaning of changes to worship space inaugurated by the Reformers.