The "Birthday of the Reformation" is often listed as 31 October 1517, when Martin Luther posted the 95 Theses on the Wittenberg Castle Church's door. This call for a debate with the established church started a chain reaction of change in Western Christendom. Following the lead of Luther, contemporary and later reformers continued to write defenses and position papers. With the Nicene, Athanasian, and Apostles' Creeds, some of these writings were gathered in the Book of Concord in 1580. These statements of belief are also known as the Lutheran Confessions, and you can find them and more at Project Wittenberg.
While the Reformation may have officially begun in 1517, it built upon earlier attempts at reform of an often corrupt and venal church. Savonarola in Italy and Hus in Bohemia led unsuccessful efforts at change. Meanwhile, the Lutheran Church itself really began to take form with the presentation of the Augsburg Confession on 25 June 1530, perhaps the official "Birthday of the Lutheran Church." From this time on, differences with Rome were clear, and both sides saw little hope in reconciliation.
The Lutheran Reformation spread to Scandinavia, and influenced the reform movement of John Calvin in France and Switzerland. It also had some impact on the English Reformation, although England saw more political than religious change.