Landwehr, or Landeswehr, is a German language term used in referring to certain national armies, or militias found in nineteenth- and early twentieth-century Europe. In different context it refers to large-scale, low-strength fortifications. In German, the word means "defence of the country"; but the term as applied to an insurrectional militia is very ancient, and lantveri are mentioned in Baluzii Capitularia, as quoted in Henry Hallam's Middle Ages, i. 262, 10th edition.

The Imperial-Royal 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. The two Landwehrs, together with the Common Army and the Imperial and Royal Navy, made up the armed forces of Austria-Hungary. While the name, "Imperial-Royal", might seem to suggest a link between the "Imperial" (Cisleithanian) and "Royal" halves of the Empire, in this context "Royal" actually refers to the Kingdom of Bohemia - 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.