Decision Support is a discipline concerned with human decision making: it aims to provide methods and tools that support, rather than replace, people in making difficult decisions. One of the widely used decision-support approaches relies on decision models, which are developed in the decision process and used to evaluate and analyse decision alternatives. In this lecture, we shall present the method DEX (Decision EXpert), which was heavily influenced by ideas from Artificial Intelligence. DEX is a hierarchical, qualitative, rule-based, multi-criteria modelling method, suitable particularly for solving classification decision problems. DEX combines traditional approaches with those from expert systems and machine learning. DEX is supported by the software called DEXi and has been used in hundreds of real-world decision-making studies. The presentation will be illustrated by recent applications in the areas of electric energy production, food safety and health care.