The marking of prisoners in the concentration camps in Nazi Germany was a complex system developed by the Nazi authorities used to group and stigmatize the prisoners in concentration camps during national socialism period. Prisoners were given a number and a special mark upon arrival at the camp, depending on race, country of origin, penalties and the like. These markings made it easier for the camp guards to identify a specific group of prisoners. The number and labeling system was also a way of dehumanizing those people because the prisoners would lose their names and identities.

Upon arrival at the camp, each prisoner was registered and given a number, which had to be sawn on his clothes. Twice a day, the prisoners were called by number.

The practice of tattooing the number on the prisoners was introduced in Auschwitz for easy identification. Specifically, in 1941 a large number of Soviet prisoners of war began arriving at the camp, and the death toll increased significantly. Because the bodies of the dead were without clothes, it was easier to register them if they had a tattoo. Tattooed numbers also made it easier to identify the escaped prisoners. In 1942, tattooing began in Birkenau. The number was usually tattooed on the left forearm, with the exception of children born in the camp whose numbers were tattooed mostly on the thigh. Those carried directly to the gas chambers did not receive numbers.

There were two series of numbers – for men and women, and later for special categories of prisoners. For example, starting from 1943, the Roma prisoners in the Bireknau camp had number but also the letter Z (German: Zigeuner - Gypsies).

The second level of marking were the triangles made of fabrics in different colors.

The marking system was standardized by 1938, although there were some variations.