The first known documentation of Dachau occurs in a medieval deed issued by the Noble Erchana of Dahauua to the prince-bishop of Freising[3], both descendants of the lineage of the Aribonids. With this deed, dated to August 15, 805 A.D. (the Feast of the Assumption of the Blessed Virgin Mary), she donated her entire property in Dachau, including five so-called Colonenhöfe and some serfs and bondsman, to devolve to the Bishop of the Diocese of Freising after her death.

6 May 1945 (23 April on the Orthodox calendar) was the day of Pascha, Orthodox Easter. In a cell block used by Catholic priests to say daily Mass, several Greek, Serbian and Russian priests and one Serbian deacon, wearing makeshift vestments made from towels of the SS guard, gathered with several hundred Greek, Serbian and Russian prisoners to celebrate the Paschal Vigil. A prisoner named Rahr described the scene:[99]
On April 26, 1945, as American forces approached, there were 67,665 registered prisoners in Dachau and its subcamps. More than half of this number were in the main camp. Of these, 43,350 were categorized as political prisoners, while 22,100 were Jews, with the remainder falling into various other categories. Starting that day, the Germans forced more than 7,000 prisoners, mostly Jews, on a death march from Dachau to Tegernsee far to the south. During the death march, the Germans shot anyone who could no longer continue; many also died of hunger, cold, or exhaustion.

At the end of July 1944 there were around 7,300 prisoners interned in the Bergen-Belsen camp complex. At the beginning of December 1944, this number had increased to around 15,000, and in February 1945 the number of prisoners was 22,000. As prisoners evacuated from the east continued to arrive, the camp population soared to over 60,000 by April 15, 1945.
In Dachau, as in other Nazi camps, German physicians performed medical experiments on prisoners, including high-altitude experiments using a decompression chamber, malaria and tuberculosis experiments, hypothermia experiments, and experiments testing new medications. Prisoners were also forced to test methods of making seawater potable and of halting excessive bleeding.
On 6 January 1942, the Soviet Minister of Foreign Affairs, Vyacheslav Molotov, sent out diplomatic notes about German atrocities. The notes were based on reports about bodies surfacing from poorly covered graves in pits and quarries, as well as mass graves found in areas the Red Army had liberated, and on witness reports from German-occupied areas.[335] The following month, Szlama Ber Winer escaped from the Chełmno concentration camp in Poland, and passed detailed information about it to the Oneg Shabbat group in the Warsaw Ghetto. His report, known by his pseudonym as the Grojanowski Report, had reached London by June 1942.[288][336] Also in 1942, Jan Karski sent information to the Allies after being smuggled into the Warsaw Ghetto twice.[337][s] On 27 April 1942, Vyacheslav Molotov sent out another note about atrocities.[335] In late July or early August 1942, Polish leaders learned about the mass killings taking place inside Auschwitz. The Polish Interior Ministry prepared a report, Sprawozdanie 6/42,[340] which said at the end:
In April 1943, a part of the Bergen-Belsen camp was taken over by the SS Economic-Administration Main Office (SS Wirtschafts-Verwaltungshauptamt; WVHA). It thus became part of the concentration camp system, run by the SS Schutzstaffel but it was a special case.[7] Having initially been designated a Zivilinterniertenlager ("civilian internment camp"), in June 1943 it was redesignated Aufenthaltslager ("holding camp"), since the Geneva Conventions stipulated that the former type of facility must be open to inspection by international committees.[8] This "holding camp" or "exchange camp" was for Jews who were intended to be exchanged for German civilians interned in other countries, or for hard currency.[9] The SS divided this camp into subsections for individual groups (the "Hungarian camp", the "special camp" for Polish Jews, the "neutrals camp" for citizens of neutral countries and the "Star camp" for Dutch Jews). Between the summer of 1943 and December 1944 at least 14,600 Jews, including 2,750 children and minors were transported to the Bergen-Belsen "holding" or exchange camp.[10]:160 Inmates were made to work, many of them in the "shoe commando" which salvaged usable pieces of leather from shoes collected and brought to the camp from all over Germany and occupied Europe. In general the prisoners of this part of the camp were treated less harshly than some other classes of Bergen-Belsen prisoner until fairly late in the war, due to their perceived potential exchange value.[9] However, only around 2,560 Jewish prisoners were ever actually released from Bergen-Belsen and allowed to leave Germany.[9]