The 66th Corps (z.b.V.) was formed on 9 May 1917. It was formerly known as Gruppe "Nowogrodek", named for the city of Nowogrodek.
With the onset of trench warfare, the German Army recognised that it was no longer possible to maintain the traditional Corps unit, that is, one made up of two divisions. Whereas at some times (and in some places) a Corps of two divisions was sufficient, at other times 5 or 6 divisions were necessary. Therefore, under the Hindenburg regime (from summer 1916), new Corps headquarters were created without organic divisions. These new Corps were designated General Commands for Special Use (German: Generalkommandos zur besonderen Verwendung).