As the global demand for rail transportation continues to grow, energy consumption and environmental impacts have increased; thus, improving the energy efficiency of rail research is necessary. Energy-efficient railways include energy-efficient trains and energy-efficient railway infrastructure. Energy-efficient driving strategies and timetable optimization are the main energy-efficient train operation measures. In addition, innovative solutions such as regenerative braking, energy storage systems and photovoltaics have been explored and implemented, and the optimization of station loads has become increasingly popular. In this paper, a framework for energy-efficient railways is proposed on the basis of previous research, and some important works on energy-efficient train operation and energy-efficient railway infrastructure are reviewed. We find that the joint optimization of energy-efficient train operations, which are related to the energy load, and energy-efficient railway infrastructure, which provides energy, is a potential way to establish energy-efficient railway systems.