The ЭД4 or ED4 is a type of electric multiple units originally developed for suburban service under 3 KV DC. It was based on the earlier ЭД2T, but this had the electric part supplied from Riga in the now independent country of Latvia. So the ЭД4 now had its electric equipment sourced from Russian companies. The mechanical part was still very similar to the ЭД2T and even the body design of the original batch was unaltered. Sets were combined of six, eight, ten, eleven or twelve cars each. Half of the cars were powered by four 235 kW traction motors. Later the ЭД4M was built with a more modern nose design, updated cabs and upgraded interiors.

In parallel to the ЭД4, the ЭД9 was built as a variant for use under 25 kV AC. One variant of the ЭД4M is the ЭД4MK, where the K stands for “comfort”. These trains are being used for longer connections over a distance of up to 700 km. Other variants were only built as prototypes, like the ЭД4M-500 with a still more modern design. Other prototypes were also built for long-distance services. The ЭД4Э (3D4E) prototype was built as an energy-saving variant with upgraded traction electronics, but also remained a one-off.