The aim of this book is to describe the main thermoeconomic diagnosis procedures developed. In chapter 2, the concepts and tools provided by Thermoeconomics for dealing with the diagnosis problem are presented and applied to an example. The aim of chapter 3 is to describe three diagnosis methods based on thermodynamic indicators: quantitative causality analysis, linear regression and neural networks. In chapters 5 and 6, these methods are applied to the diagnosis of an operating plant, which has been described in chapter 4. In order to complete the picture of thermoeconomic diagnosis, an overview of methods and systems is made in chapter 7.