German nationalism (German: Deutscher Nationalismus) is an ideological notion that promotes the unity of Germans and of the Germanosphere into one unified nation-state. It emphasises and takes pride in the patriotism and national identity of Germans as one nation and one people. German nationalism, and the concept of nationalism itself, began during the late 18th century, which later gave rise to Pan-Germanism. Advocacy of a German nation-state became an important political force in response to the invasion of German territories by France under Napoleon Bonaparte. In the 19th century, Germans debated the German question over whether the German nation-state should comprise a "Lesser Germany" that excluded the Austrian Empire or a "Greater Germany" that included the Austrian Empire or its German speaking part. The faction led by Prussian Chancellor Otto von Bismarck succeeded in forging a Lesser Germany.

Aggressive German nationalism and territorial expansion were key factors leading to both World Wars. Before World War I, Germany had established a colonial empire, which became the third-largest, after Britain and France. In the 1930s, the Nazis came to power and sought to unify all ethnic Germans under the leadership of Adolf Hitler, eventually leading to the extermination of Jews, Poles, Romani, and other people deemed Untermenschen (subhumans) in the Holocaust during World War II. After the defeat of Nazi Germany, the country was divided into East and West Germany in the opening acts of the Cold War, and each state retained a sense of German identity and held reunification as a goal, albeit in different contexts. The creation of the European Union was in part an effort to harness German identity to a European identity. West Germany underwent its economic miracle following the war which led to the creation of a guest worker program; many of these workers settled in Germany which led to tensions around questions of national and cultural identity, especially with regard to Turks who settled in Germany.

German reunification was achieved in 1990 following Die Wende, an event that caused some alarm both inside and outside Germany. Germany has emerged as a great power in Europe and in the world; its role in the European debt crisis and the European migrant crisis led to criticism of German authoritarian abuse of its power, especially with regard to the Greek debt crisis, and raised questions within and outside Germany as to its global role. Due to post-1945 repudiation of the Nazi regime and its atrocities, German nationalism has generally been viewed in the country as taboo, and people within Germany have struggled to find ways to acknowledge its past while taking pride in its accomplishments. A wave of national pride swept the country during the 2006 FIFA World Cup. Far-right parties that stress German national identity and pride have existed since the end of World War II but have never governed. According to the Correlates of War project, patriotism in Germany before World War I ranked at or near the top, whereas today it ranks at or near the bottom of patriotism surveys. However, there are also other surveys according to which modern Germany is indeed very patriotic.

Many historians have traced the first wave of German nation-building to around the year 1000. By the 13th century, a stronger sense of German identity had taken shape, and over the next two centuries the idea of a single German people, defined by common lands, language, and character, spread more widely. Scholars such as Alexander of Roes and Lupold of Bebenburg reflected on the role of the Germans within the European order and on questions of political identity.

The early 13th-century law book Sachsenspiegel contains some of the earliest references to a collective German identity. More than ten passages refer explicitly to the 'German language', the 'German lands' (including the stem duchies of Saxony, Franconia, Swabia and Bavaria), the 'history of the Germans' and 'German descent'. These four elements (language, territory, ancestry and a shared history), are regarded by some scholars as the first appearance of key features of a national consciousness within a vernacular legal text of the Middle Ages. The Sachsenspiegel also reflected ideas of 'German descent' in the context of royal elections; seven members of the Electoral College of the Holy Roman Empire were designated a privileged role in electing the Emperor, but the King of Bohemia was denied the status of chief elector on the grounds that he was not considered a German. In the Schwabenspiegel (c. 1275) this criterion was modified, requiring only partial German ancestry, which was in line with the political realities of the 1273 royal election. Later German law books, such as the Schwabenspiegel, the Deutschenspiegel [de] (c. 1275), the Freisinger Rechtsbuch (1328) and the Meißner Rechtsbuch [de] (c. 1360) continued to weave ethnic and historical elements into constitutional law. The Deutschenspiegel and Meißner Rechtsbuch emphasised four markers of German collective identity (language, territory, ancestry and a shared history), while the Schwabenspiegel and Freisinger Rechtsbuch stressed three (excluding language).

During the 15th century, German humanists began to celebrate German culture and language, and praised German achievements like Johannes Gutenberg's invention of the printing press. The humanist Jakob Wimpfeling wrote in 1502:

"There is something delightful about the happiness of being German and living in the blessed German land."

Since the start of the Reformation in the early 16th century, the German lands had been divided between Catholics and Lutherans. Partly due to the German nation being decentralised, the early German nationalist Friedrich Karl von Moser, writing in the mid-18th century, remarked that compared with "the British, Swiss, Dutch and Swedes", most Germans lacked a "national way of thinking". It was not until the concept of nationalism itself was developed by German philosopher Johann Gottfried Herder around 1770 that German nationalism began, although according to historian Wolfgang Hardtwig [de], early forms of German nationalism were already present around 1500. German nationalism was Romantic in nature and was based upon the principles of collective self-determination, territorial unification and cultural identity, and a political and cultural programme to achieve those ends. The German Romantic nationalism derived from the Enlightenment era philosopher Jean Jacques Rousseau's and French Revolutionary philosopher Emmanuel-Joseph Sieyès' ideas of naturalism and that legitimate nations must have been conceived in the state of nature. This emphasis on the naturalness of ethno-linguistic nations continued to be upheld by the early-19th-century Romantic German nationalists Johann Gottlieb Fichte, Ernst Moritz Arndt, and Friedrich Ludwig Jahn, who all were proponents of Pan-Germanism.