The Sicherheitsdienst (SD, English: "Security Service"), full title Sicherheitsdienst des Reichsführers-SS (English: "Security Service of the Reichsführer-SS"), was the intelligence agency of the SS and the NSDAP. In 1938, the SD was made the intelligence organization for the State as well as for the Party.
Between 1933 and 1939, the SD was administered as an independent SS office, after which it was transferred to the authority of the Reich Main Security Office.
The SD was mainly an information-gathering agency, while the Gestapo, and to some degree the Kriminalpolizei, were the executive agencies of the political police system. After 1938, there was also overlap with the functions of the Abwehr.