EN57 (manufacturer's designation: Pafawag 5B/6B) is an electric multiple unit used by the Polish railway operator (PKP).

SKM Trójmiasto which operates service in the Tricity area uses these units and has also modernised them, mostly to the interior.

Three class EN57 units were exported to SFR Yugoslavia in 1964, where they were classified 311-0 (for trailers) and 315-0 (for motor cars).

[1] Between 2006 and 2018, many extensive EN57 rebuilds were undertaken in which the driver's cab exteriors and headlights/taillights were replaced with new designs, among numerous other improvements, reusing only their underframes and bogies.

[2] In 2006, ZNTK "Mińsk Mazowiecki", Pesa Bydgoszcz and Newag Nowy Sącz begin rebuilding 75 EN57 units under the SPOT programme, financed by European Union funds.

The modernised units feature updated end walls, driver's cabs, and interiors, as well as accessibility improvements such as elevators for wheelchair users and enlarged toilets.

All SPOT rebuilt units will undergo another refurbishment conducted by ZNTK "Mińsk Mazowiecki" starting from 2023, to add on-board toilets in a closed system, air-conditioning in the passenger and driver cabs and CCTV cameras.

In 2008, Koleje Mazowieckie decided to rebuild 10 trainsets into EN57AKM, during which LK450X6 AC motors developed by EMIT in Żychlin were installed.

After the rebuild, these trains' top speeds were increased to 120 km/h (75 mph), with accommodations and ramps for disabled people.

Alternating current asynchronous motors were installed in the vehicles, which allowed to increase the maximum speed to 120 km/h (75 mph).

The original motors are replaced with newer asynchronous ones (in the designation they are symbolised by the letter A), the trains are equipped with air conditioning in both the driver cabs and passenger interiors, ecological toilets in a closed system, blinds in windows, LCD monitors, power sockets and (on many 2013–2018 modernisations) free on-board Wi-Fi.

EN57FPS (Feniks 57) refers to some of the last and most extensive "turbokibel" rebuilds of twenty EN57 units, done by H. Cegelski between 2015 and 2018 under contract by Polski Tabor Szynowy, Polregio and Koleje Śląskie.

[5] The unit was subsequently handed over to the ownership of the Marshal's Office of the Warmian–Masurian Voivodeship in October 2018, who then contracted out its operations to Polregio.

[7] To keep costs low, features such as air conditioning, power sockets and sometimes CCTVs and on-board toilets are often omitted from such modernisations.

[8] In 2016, Koleje Dolnośląskie contracted ZNTK "Mińsk Mazowiecki" SA to refurbish EN57-1703, in which the area of the cab windshields were optically increased by applying black paint, which gave the front of the vehicle a modern look.

Bearing in mind the value of the vehicle from the point of view of the history and development of the railway industry in Poland, the management board of Przewozy Regionalne had already in 2016 decided to withdraw the earlier decision to scrap this unit, which last saw revenue service in 2009.