The Sicherheitsdienst (SD, Security Police) was the intelligence service of the SS. The SD had been created in 1932 by Reinhard Heydrich; following the Nazi's gaining power it became a much more important organization. It was in some competition with the SA but under its chief, Heydrich, on June 9, 1934 it was made the sole "Party information service". In 1938 it was made the intelligence organization for the State as well as for the Party, supporting the Secret State Police and working with the General and Interior Administration.

The SD was tasked with the detection of actual or potential enemies of the Nazi leadership and the neutralization of this opposition. To fulfill this task, the SD created an organization of agents and informants throughout the Reich, and later throughout the occupied territories. The organization consisted of a few hundred full-time agents and several thousand informants. The SD was the information-gathering agency and the Gestapo and to a degree the Reich Kriminalpolizei were the executive agency of the political police system. Both the SD and the Gestapo were effectively under the control of Heinrich Himmler as Chief of the German Police.

In 1936 the police were divided into the Ordnungspolizei (ORPO or Regular Police) and the Sicherheitspolizei (SIPO or Security Police). The Ordnungspolizei was the Schutzpolizei (Safety Police), the Gendarmerie (Rural Police), and the Gemeindepolizei (Local Police). The Sicherheitspolizei was composed of the Reich Kriminalpolizei (Kripo) and the Geheime Staatspolizei (Gestapo). Heydrich became Chief of the Security Police and SD.

The Sicherheitspolizei was centralized in the Reichssicherheitshauptamt, (RSHA, Reich Security Main Office). The operational sections of the SD became Amt III (except for foreign intelligence which was placed in Amt VI);The Gestapo became Amt IV and the Kripo became Amt V. Ohlendorf was named the Chief of Amt III, the SD within Germany; Mueller was named the Chief of Amt IV, the Gestapo; and Nebe was named the Chief of Amt V. Later, in 1944, most of the sections of the Abwehr (military intelligence) were incorporated into Amt VI.

Heydrich was Chief of the Security Police and SD (RSHA) until his assassination in 1942, after which Ernst Kaltenbrunner became Chief. Kaltenbrunner took office on January 30, 1943 and remained there until the end of the war. The SD was declared a criminal organization after the war and its members were tried as war criminals at Nuremberg.

The SD was organised into four sections:

Section A dealt with questions of legal order and structure of the Reich and was subdivided as follows:

• A 1 General questions of work on spheres of German life.
• A 2 Law.
• A 3 Constitution and administration.
• A 4 National life in general.
• A 5 General questions of police law, and technical questions of legislation.

Section B dealt with nationality, and was subdivided as follows:

• B 1 Nationality questions.
• B 2 Minorities.
• B 3 Race and health of the people.
• B 4 Citizenship and naturalization.
• B 5 Occupied territories.

Section C dealt with culture, and was subdivided as follows:

• C 2 Educational religious life.
• C 3 Folk culture and art.
• C 4 Press, literature, radio, office for evaluation of material.

Section D dealt with economics, and was subdivided as follows:

• D a Reading office, economics, press, magazines, literature.
• D b Colonial economics.
• D S Special questions and review of material.
• D West Western occupied regions.
• D 0st Eastern occupied regions.
• D 1 Food economy.
• D 2 Commerce, handcraft, and transport.
• D 3 Finance, currency, banks and exchanges, insurance.
• D 4 Industry and Power.
• D 5 Labor and Social Questions.