The M8 is a dual voltage electric multiple unit which can run 12.5kV AC from over head lines or from 750V DC from third rail. It was designed and built by Kawasaki Heavy Industries for use on the New Haven Line section of the Metro-North Railroad. It replaces the fleet of ageing M2s, M4s and M6s.

The livery of the M8 is in the traditional exterior colours of the New Haven Line rail cars. The shape of the body on the M8 is similar to the M7 rail cars which operate on the Hudson And Harlem lines.