The topic of the dissertation is the affective phenomenon called ressentiment. Its aim is to provide a detailed account of its nature, an operational definition of the phenomenon, and a careful description of its relation to emotions, self-regarding attitudes, and values. The first task is to distinguish ressentiment from resentment, indignation, anger and hatred. A phenomenological analysis shall then provide us with an exhaustive description of this mechanism, of its relation to emotions such as envy, revenge or hatred, and of its relation to more immediate feelings of inferiority or impotence. Ressentiment alters our axiological judgements. This constitutes its most salient characteristic and is called the reevaluation process. We shall here distinguish two kinds of ressentiment based on the difference between judgement-alterations that are value-devaluations and alterations which are merely object-devaluations. We call these forms strong and weak ressentiment, respectively. In the last parts of the dissertation, we confront our theory with standard accounts of self-deception and sociological theories about the causal determinants of ressentiment.