Bundesautobahn 40 (translates from German as Federal Motorway 40, short form Autobahn 40, abbreviated as BAB 40 or A 40), (named A 430 until the early 1990s) is one of the most used Autobahns in Germany.

It crosses the Dutch-German border as a continuation of the Dutch A67 and crosses the Rhine, leads through the Ruhr valley toward Bochum, becoming B 1 (Bundesstraße 1) at the Kreuz Dortmund West and eventually merging into the A 44 near Holzwickede.

According to Der Spiegel, it is the most congested motorway in Germany.

In the city of Essen, a Stadtbahn service operates on the median of the A 40 between Tunnel Ruhrschnellweg and Mülheim-Heißen.

Between the Essen-Huttrop and the Essen-Kray junctions, there is a guided bus system called Spurbus.