Energy and the environment are inextricably linked to the economy. Thermodynamics therefore seems to be a privileged tool in overcoming the constraints associated with optimization.This first volume reports on an original, contemporary approach leading to optimal solutions in the form of trend models, proving the existence of solutions which can then be refined in a more complete and sophisticated manner.The validation of the proposed methodology is realized through real-life examples (engines, heat pumps, refrigeration systems, etc.). However, the more fundamental aspects linked to the dynamics of the transfer and conversion of energy and matter are also explored, as well as the evolution which characterizes the second law of thermodynamics.This book presents recent advances, often still undergoing research, as well as structured exercises, and is therefore aimed at both students and researchers in the field of energetics.