An abbreviation for the German phrase Wirtschafts-Verwaltungshauptamt (English: Reich Main Economic Administration), the WVHA was a Party organization under the the Schutzstaffel (SS). a historical name for the Party "Security Squadron". It was commanded by Obergruppenfuehrer Oswald Pohl.
In practice, the SS, under Heinrich Himmler was in control. Nevertheless, the dual reporting, state and party, was common, as the lines of control converged only with Adolf Hitler. Similar parallel state and party structures existed in the Soviet Union under Josef Stalin.
Created in 1942 as a merger of several other offices of the SS, March 1942, the WVHA's most infamous role was actually operating the system of concentration camps, which were seen as a source of income to the Reich, both from slave labor and confiscated goods. The SS, often termed a "state within a state", also operated various business enterprises.
Also under the WVHA were various offices that might be found in any large organization, but that made it possible for the SS to operate. These had responsibilities for finance and administration, budget, payroll, raw materials, and supplies.
Much detail about the WVHA came from the fourth of the Nuremberg Military Tribunals, a series of war crimes trials that followed the four-power International Military Tribunal of Major War Criminals. Its 1942 organization consisted of five Amtsgruppen (office groups), divided into Aemter (offices), with many field operating locations.  Pohl was sentenced to death while other officials were imprisoned, some, such as Gluecks, were never found.
WVHA Amtsgruppe A dealt with finance and administration of the WVHA and other elements of the SS. WVHA Amtsgruppe B, handled food, supplies, raw materials, and equipment for SS operations including the Waffen SS, RSHA and concentration camps. WVHA Amtsgruppe C had the responsibility for buildings, grounds, and construction, including those in concentration camps; it made much use of slave labor.
WVHA Amtsgruppe D, under the Inspector of Concentration Camps (Inspekteur der Konzentrationslager), first Theodor Eicke and then Richard Gluecks operated both the concentration and extermination camps. Since concentration camps were considered slave labor resources as well as potential sources of confiscated goods, the actual operation of the camps, as opposed to sending people to them, was under the WVHA. While security organizations such as the RSHA and Gestapo operated in the camps, they did not control them, just as the actual guards were from yet another SS organization, a division of the Waffen-SS.
WVHA Amtsgruppe W, under Pohl's direction, was responsible for SS "businesses": both the leasing of slave laborers and the operations of the SS's own enterprises.
- Nuremberg Military Tribunal 4, WVHA Organization and Officials, Introduction to NMT Case 4: U.S.A. v. Pohl et al.