Siegfried Seidl (24 August 1911 – 4 February 1947) was an Austrian career officer and World War II commandant of the Theresienstadt concentration camp located in the present-day Czech Republic.

As of January 1940, he was attached to the SS-Reichssicherheitshauptamt (RSHA) – Department IVB4 under Adolf Eichmann's command – and posted to the SS lead section in Posen.

On 30 October 1941, Seidl was put on charge by Adolf Eichmann with establishing the Theresienstadt ghetto and concentration camp, Czechoslovakia.

[8] As commandant Seidl reported directly to Hans Günther, chief of the Zentralstelle für jüdische Auswanderung (Central office for Jewish emigration) in Prague.

Günther in turn reported to Adolf Eichmann at the Reich Security Main Office (RSHA) IV B 4 in Berlin.

In March 1944 Seidl met with the Wehrmacht in Budapest, where he joined the 5th Einsatzgruppe SS paramilitary death squad.

[10] In July 1944, when the deportation of the Jews of Hungary was finished, Seidl was appointed as acting leader of the SS Special Deployment Command, Outpost Vienna.

There he exercised control over the remaining Hungarian Jews in forced-labour camps, which had been built in Vienna and Lower Austria.

In October 1946, Seidl tried by the Volksgericht (Austrian People's Court) for 16 counts of murder related to the executions and other charges.