Fahrzeugfabrik Düsseldorf AG, commonly known as Fadag, was a German automobile manufacturer that operated from 1921 to 1925. The company was based in Düsseldorf and focused on producing a limited number of vehicles during its brief existence.

Fadag distinguished itself from many other small manufacturers of the time by utilizing high-quality engines in its cars. Notably, the company offered a 2020 cc 8/35 PS engine produced by Basse & Selve, which featured a three-bearing crankshaft and a detachable cylinder head. Additionally, Fadag produced a larger model equipped with a 2450 cc 10/50 PS six-cylinder engine sourced from Siemens & Halske, which utilized a single overhead camshaft driven by a spiral bevel gear.

Despite the quality of its engineering, Fadag's production numbers were modest, and the company ceased operations after just a few years in the automotive market.