This book constitutes the proceedings of the 12th International Workshop on Communication Technologies for Vehicles, Nets4Cars/Nets4Trains/Nets4Aircraft 2017, held in Toulouse, France, in May 2017. The 12 full papers presented together with 2 demo papers in this volumewere carefully reviewed and selected from 16 submissions. The volume features contributions in the theory or practice of intelligent transportation systems (ITS) and communication technologies for: Vehicles on road: e.g. cars, tracks and buses; Air: e.g. aircraft and unmanned aerial vehicles; and Rail: e.g. trains, metros and trams.