The I Reserve Corps (German: I. Reserve-Korps / I RK) was a corps level command of the German Army in World War I. I Reserve Corps was formed on the outbreak of the war in August 1914[1] as part of the mobilisation of the Army.

[2] It was still in existence at the end of the war[3] in the 3rd Army, Heeresgruppe Deutscher Kronprinz on the Western Front.

In general, Reserve Corps and Reserve Divisions were weaker than their active counterparts In summary, I Reserve Corps mobilised with 26 infantry battalions, 11 machine gun companies (66 machine guns), 6 cavalry squadrons, 12 field artillery batteries (72 guns) and 2 pioneer companies.

36th Reserve Division was formed by units drawn from the XVII Corps District.

On mobilisation, I Reserve Corps was assigned to the 8th Army on the Eastern Front, intended to defend East Prussia while the rest of the German Army executed the Schlieffen Plan offensive against France.