The Prussian Ministry of War was the highest state authority of the Royal Prussian Army and was responsible for the central administration of the army of the Kingdom of Prussia and, later, the Imperial German Army. The ministry existed from 1808 through the establishment of the German Empire and was dissolved in 1919, being succeeded by the Ministry of the Reichswehr.

The Prussian Ministry of War was gradually established between 1808 and 1809 as part of a series of reforms initiated by the Military Reorganization Commission created after the disastrous Treaties of Tilsit. The War Ministry was to help bring the Army under constitutional review, and, along with the General Staff, systematize the conduct of warfare. Gerhard von Scharnhorst, the most prominent and influential of the reformers, served as acting Minister of War from roughly 1808 until 1810 (he was also concurrently Chief of the General Staff).

The War Ministry was established on 25 December 1808, replacing the existing military institutions. The Ministry initially consisted of two departments. The first department was responsible for the command and condition of the army, the second for its financial administration.

At first, no Minister of War was appointed due to resistance from Frederick William III, the King of Prussia. Gerhard von Scharnhorst became head of the first department (the General War Department or Allgemeines Kriegsdepartement) and Lieutenant Colonel Graf Lottum became head of the second department. Scharnhorst also functioned as acting Minister of War, as long as no permanent appointment was made.

The first department initially consisted of three divisions. The first division represented the continuation of the old Prussian Adjutancy-General and was also known as the "Privy Military Cabinet" (Geheimes Kriegskabinett). It in turn had control over the General War Chancellery (Allgemeine Kriegskanzlei). The second division dealt with general army matters, including troop formation, replacements and turnover, accommodations, military exercises and mobilization. A third division was also created, the artillery and engineering department. This in turn comprised the artillery section, which dealt with artillery equipment, rifle production, cannon foundries, powder factories, etc., and the engineering section, which was primarily responsible for the maintenance of fortifications.

The second department, the military economy department (Militär-Ökonomie Departement), had four divisions. The first division was responsible for pay, the second for provisioning, the third for clothing and the fourth for invalids.

Over the years from its founding, the structure of the Ministry of War evolved. By 1914, the ministry had the following structure:

Central Department (Zentraldepartment) (ZD)