Flossenbürg was a Nazi concentration camp built in May 1938 by the SS Main Economic and Administrative Office. Unlike other concentration camps, it was located in a remote area, in the Fichtel Mountains of Bavaria, adjacent to the town of Flossenbürg and near the German border with Czechoslovakia. The camp's initial purpose was to exploit the forced labor of prisoners for the production of granite for Nazi architecture. In 1943, the bulk of prisoners switched to producing Messerschmitt Bf 109 fighter planes and other armaments for Germany's war effort. Originally intended for German "criminal" and "asocial" prisoners, the camp's numbers swelled with political prisoners from outside Germany and, after Germany's invasion of the Soviet Union, Soviet prisoners of war. It also developed an extensive subcamp system that eventually collectively held many more prisoners than the main camp.

Before it was liberated by the United States Army in April 1945, 89,964 to 100,000 prisoners passed through Flossenbürg and its subcamps. Around 30,000 died from malnutrition, overwork, executions, or during the death marches. Some of those responsible for these deaths, including administrators, guards, and others, were tried and convicted in the Flossenbürg trial. The camp was repurposed for other uses before the opening of a memorial and museum in 2007.

During the first half of 1938, the Nazi concentration camp population expanded threefold due to increased arrests by the Schutzstaffel (SS) of individuals deemed undesirable, especially "asocial" and "criminal" prisoners, to create a slave labor force. SS leader Heinrich Himmler ordered the founding of new concentration camps to expand the SS economic empire. The SS intended to exploit the slave labor of prisoners to quarry granite, which was in high demand for monumental building projects in the Nazi style. This would also profit the SS-owned and -operated company German Earth and Stone Works (DEST), which had been founded in April.

During the second half of March 1938, a high-ranking SS commission led by Oswald Pohl and Theodor Eicke toured southern Germany, searching for a site for a new camp that would meet the SS' specifications. On 24 March 1938, they chose a site near the small town of Flossenbürg, in the Upper Palatinate, for the establishment of a concentration camp due to the quarries of blue-gray granite located nearby. Unlike all other Nazi concentration camps to date, which were near rail junctions and population centers, the camp was to be located in the remote Upper Palatine Forest near Flossenbürg Castle [de], formerly owned by Holy Roman Emperor Friedrich Barbarossa.

Flossenbürg was a poor rural area, with about 1,200 inhabitants who mostly worked on the quarries, which had existed since the 19th century. The local economy, especially the stone industry, was negatively impacted by the new border with Czechoslovakia after the Treaty of Versailles and the 1930s economic slump. Adolf Hitler's rise to power increased the demand for granite, earning the Nazi Party local support. The construction of the camp was funded by a contract with Albert Speer's ministry for the reconstruction of Berlin; it was the first occasion that economic considerations had determined the site of a camp.

The order for the construction of eight barracks at Flossenbürg went through on 31 March, SS guards arrived in April, and on 3 May 1938, a transport of 100 prisoners arrived from Dachau, establishing the camp. More prisoners arrived from Dachau on 9 and 16 May; Himmler visited the camp on 16 May with Pohl, indicating that the SS considered it an important project. The SS attempted to segregate prisoners incarcerated for criminal offences at Flossenbürg because forced labor in the quarries was considered a particularly harsh punishment. Most of the prisoners at Flossenbürg were classified as criminal, with some "asocial" and a few homosexual prisoners; the criminals quickly took over the prisoner functionary positions.

The new prisoners had to construct the camp themselves, beginning with the barbed wire fence; this was initially the main use of forced labor. While performing this heavy and dangerous work, the prisoners lived in makeshift structures. Simultaneously, hundreds of prisoners had to work in the quarries. The camp's population had increased to 1,500 following arrivals from Dachau, Sachsenhausen, and Buchenwald. In January 1939, the first commandant, Jakob Weiseborn, unexpectedly died, having committed suicide over a matter concerning his time at Buchenwald. He was replaced by a former SS officer at Dachau, Karl Künstler, who presided over an era in which the camp became an economically productive center for granite quarrying, and increasingly deadly for its prisoners. With the first barracks complete, in 1939 work began on an internal jail, guard towers, a washing facility, and a sewer system. In April 1939, the economic productivity of the camp led to Pohl ordering the camp to be expanded to fit 3,000 prisoners. To build additional barracks, terraces had to be cut into the hillsides, an arduous task that led to many injuries.

Fifty-five prisoners died before the outbreak of World War II in September 1939. During mid-1939, Nazi authorities planned to invade Poland. It was decided to stage false flag attacks in order to justify a German declaration of war. Several prisoners from Flossenbürg and other concentration camps were secretly transferred to a Gestapo prison in Breslau, poisoned, and dressed in Polish uniforms. On 31 August 1939, the bodies were dumped at a border post in Hochlinden where they were shot and hacked; photographs were taken as "proof" of a Polish attack on Germany.