Nazi Germany (officially known as the German Reich from 1933 until 1943, and the Greater German Reich from 1943 to 1945) was the German state between 1933 and 1945, when Adolf Hitler and the Nazi Party controlled the country, transforming it into a dictatorship. Under Hitler's rule, Germany quickly became a totalitarian state where nearly all aspects of life were controlled by the government. The Third Reich, meaning "Third Realm" or "Third Empire", alluded 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 Hitler and the Nazis referred to as the Thousand-Year Reich, ended in May 1945 after 12 years when the Allies defeated Germany, ending World War II in Europe.

On January 30, 1933 Hitler was formally appointed chancellor of the Weimar Republic, despite not commanding an absolute majority in the Reichstag. Hitler's appointment came about at behest of right-wing politicians and industrialists. Hitler, now acting as chancellor was still beholden to the Weimar Constitution and was subordinate to the president and head of state, Paul von Hindenburg.

Early into Hitler's chancellorship the Reichstag Building caught fire, which his government responded to by passing the Reichstag Fire Decree, leading to the suppression of civil liberties and mass arrests of German communists and other political opponents. On 23 March 1933, the Enabling Act was passed to give Hitler's government the power to make and enforce laws without the involvement of the Reichstag or president. The Nazi Party then began to eliminate all political opposition and consolidate its power. Hindenburg died on 2 August 1934, and Hitler became dictator of Germany by merging the offices and powers of the chancellery and presidency. A national referendum held 19 August 1934 confirmed Hitler as sole Führer (leader) of Germany. All power was centralised in Hitler's person and his word became the highest law. The government was not a coordinated, co-operating body, but a collection of factions struggling for power and Hitler's favour. In the midst of the Great Depression, the Nazis restored economic stability and ended mass unemployment using heavy military spending and a mixed economy. Financed by deficit spending, the regime undertook extensive public works projects, including the Autobahnen (motorways), as well as a massive secret rearmament program, forming the Wehrmacht (armed forces). The return to economic stability boosted the regime's popularity.

Racism, Nazi eugenics, and especially antisemitism were central ideological features of the regime. The Germanic peoples were considered by the Nazis to be the master race, the purest branch of the Aryan race. Discrimination and the persecution of Jews and Romani people began in earnest after the seizure of power. The first concentration camps were established in March 1933. Jews, liberals, socialists, communists, and other political opponents and undesirables were imprisoned, exiled, or murdered. Christian churches and citizens that opposed Hitler's rule were oppressed and many leaders imprisoned. Education focused on racial biology, population policy, and fitness for military service. Career and educational opportunities for women were curtailed. Recreation and tourism were organised via the Strength Through Joy program, and the 1936 Summer Olympics showcased Germany on the international stage. Propaganda Minister Joseph Goebbels made effective use of film, mass rallies, and Hitler's hypnotic oratory to influence public opinion. The government controlled artistic expression, promoting specific art forms and banning or discouraging others.

From the latter half of the 1930s, Nazi Germany made increasingly aggressive territorial demands, threatening war if these were not met. The Saarland voted by plebiscite to rejoin Germany in 1935, and in 1936 Hitler sent troops into the Rhineland, which had been demilitarized after World War I. Germany seized Austria in the Anschluss of 1938, and demanded and received the Sudetenland region of Czechoslovakia in that same year. In March 1939, the Slovak state was proclaimed and became a client state of Germany, and the German Protectorate of Bohemia and Moravia was established on the remainder of the occupied Czech lands. Shortly after, Germany pressured Lithuania into ceding the Memel Territory. Germany signed a non-aggression pact with the Soviet Union and invaded Poland on 1 September 1939, launching World War II in Europe. By late 1942, Germany and its European allies in the Axis powers controlled much of Europe and North Africa. Extended offices of the Reichskommissariat took control of Nazi-conquered areas and a German administration was established in the remainder of Poland. Germany exploited the raw materials and labour of both its occupied territories and its allies.

Genocide, mass murder, and large-scale forced labour became hallmarks of the regime. Starting in 1939, hundreds of thousands of German citizens with mental or physical disabilities were murdered in hospitals and asylums. Einsatzgruppen paramilitary death squads accompanied the German armed forces inside the occupied territories and conducted the genocide of millions of Jews and other Holocaust victims. After 1941, millions of others were imprisoned, worked to death, or murdered in Nazi concentration camps and extermination camps. This genocide is known as the Holocaust.

While the German invasion of the Soviet Union in 1941 was initially successful, the Soviet resurgence and entry of the United States into the war meant that the Wehrmacht lost the initiative on the Eastern Front in 1943 and by late 1944 had been pushed back to the pre-1939 border. Large-scale aerial bombing of Germany escalated in 1944 and the Axis powers were driven back in Eastern and Southern Europe. After the Allied invasion of France, Germany was conquered by the Soviet Union from the east and the other Allies from the west, and capitulated on 8 May 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 victorious Allies initiated a policy of denazification and put many of the surviving Nazi leadership on trial for war crimes at the Nuremberg trials.