Protestantism (German: Protestantismus), a branch of Christianity, was founded within Germany in the 16th-century Reformation. It was formed as a new direction from some Roman Catholic principles. It was led initially by Martin Luther and later by John Calvin.

The Protestant Reformation began with the publication of the Ninety-five Theses by Augustinian friar Martin Luther in 1517. The key element of this religious upheaval was a break from Roman Catholicism's emphasis on tradition, favouring a focus on the Bible. The lasting effects of Luther's Protestant movement within Germany was to question its existing power structures, imploring lay nobles for church reformation, critiquing the Roman mass, sacraments and seeking to reaffirm the importance of faith in good works. His subsequent excommunication from the Church ensured Germany had an ideological divide between Protestant sects and other Christian denominations. Another prominent reformer, Martin Bucer, introduced the rite of communion to German Protestantism and promoted Protestant unity, ensuring the anti-Baptist sect re-joined the wider church. John Calvin, whose writings formulated the Calvinist movement, emphasised the importance of Old Testament Law. Luther called upon the assistance of German princes to further the Protestant movement, namely Phillip of Hesse who convened the Marburg Colloquy where key Protestant theologians agreed on theological questions relevant to Germany. The Marburg Colloquy reforms included a restructuring of the Protestant Church in the light of the early church, the dissolution of monastic communities, establishment of Protestant universities, the regular inspection of Parishes and the conversion of nuns and monks. The Thirty Years' War, which took place from 1618 to 1648, stunted the theological development of Protestantism in Germany due to the severe reduction in population it triggered, with estimates suggesting as much as 90% of the German population was lost and barbary was common.

Lutheranism spread in Germany through the work of Martin Luther. Lutheranism teaches three sacraments, including baptism, confession and absolution, and eucharist. The Independent Evangelical-Lutheran Church is a Confessional Lutheran body in Germany. A number of Lutheran monasteries, convents and religious orders are present in Germany, such as the Priory of St. Wigbert.

Continental Reformed Protestantism spread in Germany, originating through the efforts of the reformer John Calvin. Reformed Christianity (Calvinism) gained support in Germany in 1604 when Maurice, Landgrave of Hesse-Kassel converted from Lutheranism. His conversion prompted serious backlash against the Calvinists from the predominantly Lutheran population in Hesse. In 1613, the Reformed gained another prominent convert, John Sigismund, Elector of Brandenburg. Eventually, Brandenburg would become a bi-confessional state, allowing for both Lutheranism and Calvinism, and the Electors of Brandenburg often advocated for their persecuted Reformed (Calvinist) brethren.

Reformed Christianity upholds covenant theology.

Two Reformed denominations are members of the EKD in Germany including the Evangelical Reformed Church in Germany and the Church of Lippe.

In the early 1500s, the Holy Roman Empire led by Charles V treated German Protestantism as a competitor to its geo-political power, issuing a decree in 1524 banning the recitation of its Lutheran works. This prompted riots across Germany and in 1529 a formal protestation was issued by a body of Protestant leaders and Princes, claiming the need for a clear separation from the Imperial Diet and the right to autonomy. In February 1531, prominent Protestant Princes formed the League of Schmalkalden, endorsed by Luther, with the intent to defend the rights of princes and the religion. The league became central to the spread of Protestantism by using its political sway in Germany, helping the restoration of the Lutheran Duke of Wurttemberg in 1534, enabling the establishment of Protestantism in the region. Conflicts with the Holy Roman Empire, resolved by the 1548 Council of Trent, maintained a lack of concessions to the German Protestants, and country-wide riots ensured it was not accepted. The official separation of Protestantism and the state in Germany came with the adoption of the Weimar Constitution in 1919.

In the 19th century, Johann Hinrich Wichern pioneered a Protestant movement, the Inner mission, that sought a rebirth of the Church in Germany but also a greater emphasis on gaining support for social welfare and relief programs among Protestants. Throughout the 19th century Protestant churches in Germany were reactionary and politically conservative. Protestant theologians rejected the tenets of the French Revolution, seeing instead an increase in nationalism. This nationalism, was combined with piety, evidenced by the notable addresses of Johann Gottlieb Fichte's "Address to the German Nations" and Ernst Moritz Arndt's writings against Napoleon Bonaparte.