X3 is an electric multiple unit train used by Arlanda Express on the airport rail link service between Stockholm Central Station and Stockholm-Arlanda Airport in Sweden. Alstom built seven of these four-car units in Birmingham, which were delivered in 1998 and 1999. The X3 is part of the Coradia family, and can reach speeds up to 205 km/h.
The trains are painted grey with yellow ends with varying interior colors. The units use standard gauge tracks and are fed electricity at 15 kV 16⅔ Hz AC like the rest of the Swedish railway network, but the trains use separate stations at Arlanda and dedicated tracks at Stockholm C; in both cases, the platforms are higher than at other stations in Sweden, allowing step-free access to the trains without the use of low floors.