The book has been conceived to convey the fundamentals of numerical simulation to students of Engineering and Business Schools, to facilitate the application of numerical simulation to decision making in the field of management, and to enable professionals to use a methodology for decision making that allows them to evaluate the behavior of their organization against the different decisions they can adopt, so they can choose the best alternative. One of the book's main challenges is to capacitate the reader to build models of real situations and to carry out experiments without specific software, which will enable him or her to create his own models and adopt the best possible decisions. Simulation is an analysis tool that allows to draw conclusions about a real system without having to work directly with it. The advancement of software tools, especially spreadsheets, allows complex simulations to be carried out on a simple spreadsheet accessible to any computer, giving decision-makers the ability to evaluate the behavior of a system against their decisions before taking them, without affecting the system and at practically zero cost