Book briefly discusses decision-making basic theory, in particular the deliberation method, and applies it to decision-making in the mining sector when making investment agreements between government and the private sector. However, decisions could be examined and applied in every industry sector. For instance, the mining sector includes many different decision making methods such as cost benefit analysis and socio-economic, environmental and health impact assessments. Every analysis and impact assessment requires different stakeholder participants and analysts from different sciences. This can sometimes make decisions more complicated. My book analyzes the planned Oyu Tolgoi (OT) copper and gold project in Mongolia using the Multi Account Evaluation method, which includes financial, economical, social and environmental analysis. It also briefly discusses social and environmental impacts from the Mongolian government point of view and whether this project will have a positive or negative influence on Mongolian economic and social development. My thesis also shows the current Mongolian decision-making situation and its problems.