European route E40 is the longest European route,[1] more than 8,000 kilometres (4,971 miles) long, connecting Calais in France via Belgium, Germany, Poland, Ukraine, Russia, Kazakhstan, Uzbekistan, Turkmenistan, and Kyrgyzstan, with Ridder in Kazakhstan near the border with Russia and China.

A different route, connecting Calais and Ridder, is about 2,000 kilometres (1,243 miles) shorter, mostly using the E30 via Berlin-Moscow-Omsk.

The E40 differs from that route in order to provide additional direct east–west access to Uzbekistan, Turkmenistan, and Kyrgyzstan, with a combined population base approaching 50 million people as of 2021.

Since 2014, parts of the road in eastern Ukraine have been under the control of the separatist Donetsk People's Republic and Lugansk People's Republic.

During the 2022 Russian invasion of Ukraine, Russia took direct control of the areas in Donbas.