The Evolution Series is a line of diesel locomotives built by GE Transportation Systems, initially designed to meet the U.S. EPA's Tier 2 locomotive emissions standards that took effect in 2005. The first pre-production units were built in 2003. Evolution Series locomotives are equipped with either AC or DC traction motors, depending on the customer's preference. All are powered by the GE GEVO engine.
The Evolution Series was named as one of the "10 Locomotives That Changed Railroading" by industry publication Trains Magazine. It was the only locomotive introduced after 1972 to be included in that list. The Evolution Series, mainly the ES44DC, ES44AC, and ET44AC, are some of the best-selling and most successful freight locomotives in United States history.