In this paper, the objectives of thermoeconomic diagnosis are presented. The paper is part of a project, started in 2001 and named TADEUS (Thermoeconomic Approach to the Diagnosis of Energy Utility Systems), aimed at integrating various experiences accumulated by a group of researchers working on thermoeconomic diagnostics, a field of research started by Antonio Valero and co-workers in 1990 and followed by various researchers all over the world. It is shown how, starting from the same basic set of ideas, researchers developed different approaches, each one having particular characteristics that are, nonetheless, complementary to each other.