This book contains the fundamentals of economic science that every undergraduate student should know and that will help him/her to improve his/her way of thinking and understanding the economic reality. Therefore, we begin with an overview of the concept, field of economics and its division. Generally, economic science comprises two major branches of study: Microeconomics (or Theory of Price Formation) and Macroeconomics (or Theory of Economic Aggregates). The first deals with topics such as demand, supply, market structure and its implications in daily life, under a neoclassical approach. While the second branch is at the aggregate level, where the participation of the government stands out, through Fiscal and Monetary Policy, which impacts the decisions of the other economic agents (families, companies and the rest of the world).