Demag (In German Deutsche Maschinenbau-Aktiengesellschaft) was a German heavy equipment industrial group whose individual companies are now scattered. The Demag name can be today found for example as the Demag Cranes and Components and Sumitomo (SHI) Demag.

The roots of Demag date back prior to its formation, but became Märkische Maschinenbau-Anstalt, Ludwig A.-G in 1906 as the biggest crane building company in Germany employing 250-300 people. The company was a manufacturer of industrial cranes that included types like, bridge cranes, hoist (device), overhead cranes, Gantry crane to name a few. In 1910 came the hour of the Deutsche Maschinenfabrik in Duisburg – known worldwide by its telegram abbreviation Demag (now Demag Cranes & Components GmbH).

In 1973 The Mannesmann group assumed ownership of Demag.

The Demag company was formed finally 1910 in Duisburg through the union of the Märkische Maschinenbau-Anstalt L. Stuckenholz AG, the Duisburg Mechanical Engineering AG, and the Benrath Machine Works GmbH.

The Märkische Maschinenbau-Anstalt L. Stuckenholz AG traces back to the machine factory Mechanische Werkstätten Harkort & Co., founded 1819 in Wetter an der Ruhr, already beginning the manufacturing of cranes in 1840.

In 1908, they designed what was then the world's largest floating crane, built for Harland & Wolff in Belfast, which would be used for the building of the passenger liners RMS Olympic and RMS Titanic.

Starting in 1925, Demag also manufactured excavators. They expanded to manufacture locomotives and railroad cars. During the Second World War, armoured fighting vehicles (in particular Bergepanther) were built in the Berlin Staaken plant.

During the buildup to, and during World War II, Demag-designed halftrack military vehicles, both in unarmored "artillery tractor" models in the late 1930s, the basis for the powertrain of their armored Sd.Kfz. 250, which itself played an important role during the war, with just over 6,600 built by Demag and their subcontractors.