The purpose of this text is to provide a critical thinking framework for all individuals utilizing decision and evaluation models, whether it be for research or applications. It is axiomatic that all evaluation and decision models suffer some limitations. There are situations where a decision model will not perform to expectations. This book argues that there is no best decision or evaluation model, but that decision-makers must understand the principles of formal evaluation and decision models and apply them critically. Hence, the book seeks to deepen our understanding of evaluation and decision models and encourage users of these models to think more analytically about them. The authors work in six different European universities. Their backgrounds are varied: mathematics, economics, engineering, law, and geology, and they teach in engineering, business, mathematics, computer science, and psychology in their universities. As a group, the authors have particular expertise in a variety of decision models that include preference modelling, fuzzy logic, aggregation techniques, social choice theory, artificial intelligence, problem structuring, measurement theory, operations research, and multiple criteria decision support. In addition to their decision analysis research, all the authors have been involved in a variety of high-impact applications which include software evaluation, location of a nuclear repository, the rehabilitation of a sewer network, and the location of high-voltage lines. It is this variety within the authorship that unifies this book into a systematic examination of how best formal decision models can be used. The monograph should prove a useful tool for researchers of decision analysis and decision-makers.