The long-term forecasting of energy supply and demand is one of the most important topics to Mongolia due to the country's abundant natural resources, which offer great opportunities for achieving independent, sustainable, and green energy development if managed properly. In this book, an overview of the current situation of Mongolia's energy sector and its role and contribution in the country's economy and the environment, and also comprehensive assessment of the sector, are provided. Most importantly, the long-range energy alternatives planning system (LEAP) model was used to forecast the future energy supply and demand by establishing and comparing possible scenarios to 2040.