Friedrich "Fritz" Hartjenstein (July 3, 1905 - October 20, 1954) was an SS-Obersturmbannführer (Lieutenant Colonel).

Born in Peine, he began concentration camp service at Sachsenhausen in 1938. The following year, he was transferred to Niedernhagen . In 1941, he was assigned to the 3rd SS Division "Totenkopf", where he served for a year.

In 1942, he was appointed the commandant of Birkenau, the death camp in Auschwitz. He holds responsibility for hundreds of thousands of gassings. In 1944, he was transferred to Natzweiler concentration camp and appointed the commandant. He was subsequently transferred to Flossenbuerg , serving as commandant.

Hartjenstein's postwar fate consisted of many trials. First, he was arrested by the British and sentenced to life imprisonment on June 1, 1946 at Wuppertal for executing four resistance members. Then he was again tried by the British for hanging a POW who was a member of the Royal Air Force and sentenced to death by firing squad on June 5 of that year. He was then extradited to France, where he was tried for his crimes at Natzweiler and sentenced to death. He died of a heart attack while awaiting execution on October 20, 1954.