Armee-Korps) was a corps level command of the German Army before and during World War I.

XX Corps served on the Eastern Front from the start of the war.

The 25 peacetime Corps of the German Army (Guards, I - XXI, I - III Bavarian) had a reasonably standardised organisation.

Divisions received engineer companies and other support units from the Corps headquarters.

Immediately after 1st Masurian Lakes it joined 9th Army in Lower Silesia where it fought at the Battle of the Vistula River.