The Imperial-Royal Landwehr (German: kaiserlich-königliche Landwehr or k.k. Landwehr), also called the Austrian Landwehr, was the territorial army of the Cisleithanian or Austrian half of the Austro-Hungarian Empire from 1869 to 1918. Its counterpart was the Royal Hungarian Landwehr (k.u. Landwehr). The two Landwehrs, together with the Common Army and the Imperial and Royal Navy, made up the armed forces (Bewaffnete Macht or Wehrmacht) of Austria-Hungary. While the name, "Imperial-Royal", might seem to suggest a link between the "Imperial" (Cisleithanian) and "Royal" (Transleithanian or Hungarian) halves of the Empire, in this context "Royal" actually refers to the Kingdom of Bohemia (Königreich Böhmen or České království) - not a sovereign kingdom on par with the Kingdom of Hungary, but a crownland of Cisleithanian Austria-Hungary and possession of the Habsburgs, who remained formally entitled to kingship. In this sense, the Kingdom of Bohemia was comparable in status to the Kingdom of Galicia and Lodomeria and the Kingdom of Dalmatia.

Unlike the German Empire, where the Landwehr mainly comprised reservists and volunteers, the Imperial-Royal Landwehr consisted of regular units. It was fully established with regular troops and not partly mobilized or cadred. The Landwehr should not be confused with the Landsturm which was a volunteer militia.

The roots of the Landwehr go back to the 16th century when there were calls on all able-bodied men to defend their country.

During the Napoleonic Wars a Landwehr was established by imperial decree dated 9 June 1808 as a standing and common institution to complement the regular Austrian army. This army was used in 1809 and in 1813/14. In 1859, the Landwehr was abolished.

After the Austrian Empire had lost the war against Prussia, the Austro-Hungarian Compromise put an end of the unitary Austrian rule over Hungary and established the Dual Monarchy. Hungary now wanted its own forces under command of the Hungarian government alongside the existing Imperial and Royal Army and Navy, which were commanded by the Emperor and Austro-Hungarian Minister of War. So the Compromise included the right of Hungary to establish the Royal Hungarian Landwehr (Magyar Királyi Honvédség), often colloquially known as the Honved or Honvéd (Honvédség).

As a consequence, the Cisleithanian counterpart of the Honved, known as the Imperial-Royal Landwehr, was established in the "kingdoms and lands represented in the Reichsrat", i.e. the remaining Empire of Austria. Its tasks were finally confirmed in 1889 in the Austrian Defence Act (RGBl. 41/1889) as follows:

§ 4. The Landwehr is tasked in time of war to support the Army and to defend the homeland; in peacetime, and by exception, also to maintain law and order and security of the homeland.

In § 14 Wehrgesetz 1889 the annual recruiting quota for the Landwehr was set at 10,000 men.