Energy utilization systems and the related conversion technologies are evaluated from the thermodynamic view point in order to regulate the energy flow path. Involvement of thermal energy, directly as well as indirectly in any conversion process or operation is discussed, indicating that an innovative advancement of conversion technologies between heat and other forms of energy may be a breakthrough for ultimate energy utilization. Such highly efficient conversion technologies for the respective steps along the energy flow path, namely primary energy conversion, energy transportation and energy utilization including storage and recovery, are discussed.