The Nazi term Gleichschaltung (German pronunciation: [ˈɡlaɪçʃaltʊŋ] ^ⓘ), meaning "synchronization" or "coordination", was the process of Nazification by which Adolf Hitler—leader of the Nazi Party in Germany—established a system of totalitarian control and coordination over all aspects of German society "from the economy and trade associations to the media, culture and education".

Although the Weimar Constitution remained nominally in effect throughout Hitler's dictatorship, near total Nazification was achieved by 1935 with the resolutions approved during that year's Nuremberg Rally, fusing the symbols of the party and the state (see Flag of Nazi Germany) and depriving German Jews of their citizenship (see Nuremberg Laws). The tenets of Gleichschaltung, including the Nuremberg Laws, also applied to territories occupied by the German Reich.

Gleichschaltung is a compound word that comes from the German words gleich (same) and Schaltung (circuit) and was derived from an electrical engineering term meaning that all switches are put on the same circuit allowing them all to be simultaneously activated with a master switch. Its first use is credited to Reich Justice Minister Franz Gürtner. It has been variously translated as "coordination", "Nazification of state and society", "synchronization", and "bringing into line". English texts often use the untranslated German word to convey its unique historical meaning. In their seminal work on National Socialist vernacular, Nazi-Deutsch/Nazi-German: An English Lexicon of the Language of the Third Reich, historians Robert Michael and Karin Doerr define Gleichschaltung as: "Consolidation. All of the German Volk's social, political, and cultural organizations to be controlled and run according to Nazi ideology and policy. All opposition to be eliminated." This accords with the general description provided by historian Jane Caplan, who characterized the term as "the coordination of German institutions into a cohesive, Nazified whole".

The Nazis were able to put Gleichschaltung into effect due to multiple legal measures enacted by the Reich government during the 19 months following 30 January 1933, when Adolf Hitler became Chancellor of Germany. These decrees, acts and laws built an edifice of apparent legality by which the organs of government, and the levers of political power, were brought under the control of the Nazis and Hitler.

When Hitler was appointed Reich Chancellor on 30 January 1933, the Nazi Party held the leadership of only four of the 17 German Länder (states), i.e., Anhalt, Oldenburg, Mecklenburg-Schwerin and Thuringia. But the Nazis acted swiftly to eliminate any potential centers of opposition in the remaining states. Immediately after the Reichstag election of 5 March 1933, the central government began in earnest its campaign to take over the state governments it did not yet control, and within a very short period it achieved dominance over the administration in every state.

The pattern was in each case similar: pressure on the non-Nazi state governments to place a National Socialist in charge of the police; threatening demonstrations from SA and SS troops in the big cities; the symbolic raising of the swastika banner on town halls; the capitulation with hardly any resistance of the elected governments; the imposition of a Reich Commissar under the pretext of restoring order ... Despite the semblance of legality, the usurpation of the powers of the Länder by the Reich was a plain breach of the Constitution. Force and pressure by the Nazi organizations themselves—political blackmail—had been solely responsible for creating the 'unrest' that had prompted the alleged restorations of 'order'. The terms of the emergency decree of 28 February provided no justification since there was plainly no need for defence from any 'communist acts of violence endangering the state'. The only such acts were those of the Nazis themselves.

Most coalition cabinets that the Nazis formed were with the participation of their conservative nationalist ally, the German National People's Party (DNVP). The "Law Against the Founding of New Parties" (14 July 1933) banned all parties except the Nazi Party. The DNVP members of the remaining coalition cabinets eventually either joined the Party or were replaced by Nazis, resulting in one-party government in all the Länder.

The following table presents an overview of the process of Gleichschaltung as it was applied to the Nazification of the German Länder governments. While, strictly speaking, Gleichschaltung did not start until after the Nazi seizure of power at the Reich level at the end of January 1933, the table also presents earlier Nazi Party successes in infiltrating and taking charge of several German state administrations during 1930–1932. In most of these instances, they took the portfolio of the state interior ministries from which they controlled the police, installing Nazi adherents and purging opponents.