Diesel electric, electricity or steam power are the three major fuels used by trains. As it was in various other sectors, steam power was also used in the beginning days of railroads. The development of diesel-electric and electric technology for power led to their popularity in the early 20th century.

Trains use a variety of energy sources depending on their age, location, and purpose, but the two primary forms are diesel and electricity. Diesel-electric locomotives are common in North America; they use a diesel engine to turn an alternator, which generates electricity to power the traction motors on the wheels. In Europe and Asia, high-speed and commuter rail systems are primarily fully electric, drawing power from overhead catenary wires or a "third rail" on the ground. This electricity can be sourced from a mix of coal, natural gas, nuclear, or increasingly, renewable sources like wind and solar. In 2026, the industry is seeing a massive shift toward Hydrogen Fuel Cells (like the Alstom Coradia iLint) and Battery-Electric trains for "non-electrified" branch lines to eliminate carbon emissions. There are even experimental "Gravity Trains" used in mining that use the energy of descending downhill to charge batteries that power the trip back up. Traditional steam coal is now almost exclusively reserved for heritage and tourist railroads.