The Ministry for State Security, commonly known as the Stasi (German: [ˈʃtaːziː] (listen)), was the state security service of East Germany from 1950 to 1990.

The Stasi's function was similar to that of the KGB, serving as a means of maintaining state authority, i.e., the "Shield and Sword of the Party" (Schild und Schwert der Partei). This was accomplished primarily through the use of a network of civilian informants. This organization contributed to the arrest of approximately 250,000 people in East Germany. The Stasi also conducted espionage and other clandestine operations abroad through its subordinate foreign intelligence service, the Office of Reconnaissance, or Head Office A (German: Hauptverwaltung Aufklärung). They also maintained contacts and occasionally cooperated with West German terrorists.

The Stasi was headquartered in East Berlin, with an extensive complex in Berlin-Lichtenberg and several smaller facilities throughout the city. Erich Mielke was the Stasi's longest-serving chief, in power for 32 of the 40 years of the GDR's existence. The HVA (Hauptverwaltung Aufklärung), under Markus Wolf, gained a reputation as one of the most effective intelligence agencies of the Cold War.

After German reunification, numerous officials were prosecuted for their crimes and the surveillance files that the Stasi had maintained on millions of East Germans were unclassified so that all citizens could inspect their personal files on request. The files were maintained by the Stasi Records Agency until June 2021, when they became part of the German Federal Archives.