Auschwitz-Birkenau was the largest of Nazi Germany’s concentration camps.
The camp took its name from the nearby town of Oswiecim (Auschwitz in German).
Birkenau, the German translation of Brzezinka, refers to the many birch trees surrounding the complex.

The Auschwitz-Birkenau State Museum estimates the death toll at 1.1 million, about 90 percent of whom were Jews from almost every country in Europe. Most victims were killed in Auschwitz II’s gas chambers using Zyklon B; other deaths were caused by systematic starvation, forced labor, lack of disease control, individual executions, and purported "medical experiments".

The three main camps were:
(1) Auschwitz I, the original concentration camp which served as the administrative center for the whole complex, and was the site of the deaths of roughly 70,000 people, mostly Poles and Soviet prisoners of war.
(2) Auschwitz II (Birkenau), an extermination camp or Vernichtungslager, where at least 960,000 Jews, 75,000 Poles, and some 19,000 Roma (Gypsies) were killed. Birkenau was the largest of all the Nazi extermination camps.
(3) Auschwitz III (Monowitz), which served as a labor camp for the Buna-Werke factory of the I.G. Farben concern.