Energy is one of the priority development objectives for the countries. Changing environmental and climate conditions force countries to meet their energy needs. Energy should be low-cost, sustainable and reliable to meet the rapidly rising demand. Since energy is a substantial input for all sectors, improvements in this area directly affect the sectors. Therefore, there is a need for optimization applications to be performed in this subject. Energy has an interdisciplinary application area, so the integration of different engineering problems requires optimization applications. In this study, optimization problems of energy field are discussed, and energy problems are classified by decision level, application area and energy type. In addition, the related literature is analysed with regard to model structures and solution methods. The paper provides an overview of the applications of energy optimization techniques in order to guide researchers studying in this area.