This course introduces students to the fundamentals of Operations Research / Management Science and aims to present the decision-making process and its applications for solving complex business problems. Specifically, it deals with creating conceptual backgrounds, mathematical models (e.g., models, methodologies, techniques, concepts, systems, etc.) and the development of tools for systematic decision-making in real business situations. Focus is given on examining and understanding the various models, their applications in various areas of operation, intuitive and their economic importance in decision-making and the application of modern software tools in decision-making. The course will cover 3 main categories, namely linear programming models, integer programming models and decision trees, while in parallel it will refer to multi-criteria and simulation models. Together with the theory and methodology, for each model category the students will be exposed to the use of software tools, based mainly on Microsoft Excel, and they will have the opportunity to test their skills on various problem settings.