Nazi Germany, officially the German Reich and later the Greater German Reich, was the German state between 1933 and 1945, when Adolf Hitler and the Nazi Party controlled the country, transforming it into a totalitarian dictatorship. The Third Reich, meaning "Third Realm" or "Third Empire", referred to the Nazi claim that Nazi Germany was the successor to the earlier Holy Roman Empire (800–1806) and German Empire (1871–1918). The Third Reich, which the Nazis referred to as the Thousand-Year Reich, ended in May 1945, after 12 years, when the Allies defeated Germany and entered the capital, Berlin, ending World War II in Europe.

After Hitler was appointed Chancellor of Germany in 1933, the Nazi Party began to eliminate political opposition and consolidate power. A 1934 German referendum confirmed Hitler as sole Führer (leader). Power was centralised in Hitler's person, and his word became the highest law. The government was not a co-ordinated, cooperating body, but rather a collection of factions struggling to amass power. To address the Great Depression, the Nazis used heavy military spending, extensive public works projects, including the Autobahnen (motorways) and a massive secret rearmament program, forming the Wehrmacht (armed forces), all financed by deficit spending. The return to economic stability and end of mass unemployment boosted the regime's popularity. Hitler made increasingly aggressive territorial demands, seizing Austria in the Anschluss of 1938, and the Sudetenland region of Czechoslovakia. Germany signed a non-aggression pact with the Soviet Union and invaded Poland in 1939, launching World War II in Europe. In alliance with Fascist Italy and other Axis powers, Germany conquered most of Europe by 1940 and threatened Britain.

Racism, Nazi eugenics, anti-Slavism, and especially antisemitism were central ideological features of the regime. The Nazis considered Germanic peoples to be the "master race", the purest branch of the Aryan race. Jews, Romani people, Slavs, homosexuals, liberals, socialists, communists, other political opponents, Jehovah's Witnesses, Freemasons, those who refused to work, and other "undesirables" were imprisoned, deported, or murdered. Christian churches and citizens that opposed Hitler's rule were oppressed and leaders imprisoned. Education focused on racial biology, population policy, and fitness for military service. Career and educational opportunities for women were curtailed. The Nazi Propaganda Ministry disseminated films, antisemitic canards, and organised mass rallies, fostering a pervasive cult of personality around Hitler to influence public opinion. The government controlled artistic expression, promoting specific art forms and banning or discouraging others. Genocide, mass murder, and large-scale forced labour became hallmarks of the regime; the implementation of the regime's racial policies culminated in the Holocaust.

After invading the Soviet Union in 1941, Nazi Germany implemented the Generalplan Ost and Hunger Plan, as part of its war of extermination in Eastern Europe. The Soviet resurgence and entry of the United States into the war meant Germany lost the initiative in 1943 and by late 1944 had been pushed back to the 1939 border. Large-scale aerial bombing of Germany escalated and the Axis powers were driven back in Eastern and Southern Europe. Germany was conquered by the Soviet Union from the east and the other allies from the west, and capitulated in 1945. Hitler's refusal to admit defeat led to massive destruction of German infrastructure and additional war-related deaths in the closing months of the war. The Allies subsequently initiated a policy of denazification and put many of the surviving Nazi leadership on trial for war crimes at the Nuremberg trials.

Common English terms for the German state in the Nazi era are "Nazi Germany" and the "Third Reich", which Hitler and the Nazis also referred to as the "Thousand-Year Reich" (Tausendjähriges Reich). The latter, a translation of the Nazi propaganda term Drittes Reich, was first used in Das Dritte Reich, a 1923 book by Arthur Moeller van den Bruck. The book counted the Holy Roman Empire as the first Reich and the German Empire as the second.

Severe setbacks to the German economy began after World War I ended, partly because of reparations payments required under the 1919 Treaty of Versailles. The government printed money to make the payments and to repay the country's war debt, but the resulting hyperinflation led to inflated prices, economic chaos, and food riots. When the government defaulted on their reparations payments in January 1923, French troops occupied German industrial areas along the Ruhr and widespread civil unrest followed.

The National Socialist German Workers' Party, commonly known as the Nazi Party, was founded in 1920. The Nazi party platform included destruction of the Weimar Republic, rejection of the Treaty of Versailles, radical antisemitism, and anti-Bolshevism. They promised a strong central government, increased Lebensraum ("living space") for Germanic peoples, formation of a national community based on race, and racial cleansing via the active suppression of Jews, who would be stripped of their citizenship and civil rights. The Nazis proposed national and cultural renewal based upon the Völkisch movement. The party, especially its paramilitary organisation Sturmabteilung (SA; Storm Detachment), or Brownshirts, used physical violence to advance their political position, disrupting the meetings of rival organisations and attacking their members as well as Jewish people on the streets. Such far-right armed groups were common in Bavaria, and were tolerated by the sympathetic far-right state government of Gustav Ritter von Kahr.

When the stock market in the United States crashed in 1929, the effect in Germany was dire. Millions were thrown out of work and several major banks collapsed. Hitler and the Nazis prepared to take advantage of the emergency to gain support for their party. They promised to strengthen the economy and provide jobs. Many voters decided the Nazi Party was capable of restoring order, quelling civil unrest, and improving Germany's international reputation. After the federal election of 1932, the party was the largest in the Reichstag, holding 230 seats with 37.4 per cent of the popular vote.