Ressentiment (full German title: Über Ressentiment und moralisches Werturteil) is a 1912 book by Max Scheler (1874–1928), who is sometimes considered to have been both the most respected and neglected of the major early 20th-century German Continental philosophers in the phenomenological tradition. His observations and insights concerning "a special form of human hate" and related social and psychological phenomenon furnished a descriptive basis for his philosophical concept of "Ressentiment". As a widely recognized convention, the French spelling of this term has been retained in philosophical circles so as to preserve a broad sense of discursive meaning and application. Scheler died unexpectedly of a heart attack in 1928 leaving a vast body of unfinished works. Extrapolations from his thoughts have always since piqued interest and discussion on a variety of topics. His works were on the Nazi book burn list.

As a concept belonging to the study of ethics, Ressentiment represents the antithetical process of Scheler's emotively informed non-formal ethics of values. But Ressentiment can also be said to be, at once, Scheler's darkest as well as his most psychological and sociological of topics, foreshadowing many later findings in those particular social sciences.

Folk wisdom comes closest to Scheler's meaning by recognizing Ressentiment as a self-defeating turn of mind which is non-productive and ultimately a waste of time and energy. Maturity informs most of us that sustained hatred hurts the hater far more than the object of our hate. Sustained hatred enslaves by preventing emotional growth from progressing beyond the sense of pain having been precipitated, in some way, by whom or what is hated (i.e., another person, group or class of persons).

It is difficult to imagine the intellectual concern of the late 19th and early 20th century over the collective drift in Western civilization away from old-guard monarchical and hierarchical societal structures (i.e., one's station in life being determined primarily by birth), toward the relative uncertainty and instability embodied in such Enlightenment era ideals as democracy, nationhood, class struggle (Karl Marx), human equality, humanism, egalitarianism, utilitarianism, and the like. As such, Ressentiment, as a phenomenon, was first viewed as a pseudo-ethically based political force enabling the lower classes of society to rise in their situation in life at the (perceived) expense of the higher or more inherently "noble" classes. Hence, Ressentiment first emerged as what some might view a reactionary and elitist concept by today's democratic standards; while others of a more conservative mind-set might view Ressentiment as liberalism disguised as a socialist attempt at usurping the role of individual responsibility and self-determination. In any event, Scheler's contributions regarding this topic can not be fully appreciated without some cursory reference to the thought of Friedrich Nietzsche (1844–1900).

Friedrich Nietzsche used the term Ressentiment to explain this emerging degenerative morality issuing from an underlying existential distinction between what he saw as the two basic character options available to the individual: the Strong (the "Master") or the Weak (the "Slave"). The Master-type fully accepts the burdens of freedom and decides a path of self-determination. The Slave, rather than deciding to be the authentic author of their own destiny, chooses a repressed unsatisfying mode of life, blaming (by projection) his submissiveness, loss of self-esteem and pitiful lot in life upon the dominant Master figure (and their entire social class) who by contrast seems to flourish at every moment. A true enough assessment, given that economic exploitation always seems to lie at the heart of any intrinsic Master / Slave social arrangement, along with the Master class "washing their hands" (so to speak) of the burdens of social responsibility. This underlying Ressentiment forms the underlying rationale for a code of conduct (e.g., passive acceptance of abuse, fear of reprisal for asserting personal rights due to implied intimidation, or inability to enjoy life) belonging to the Slave-type or class ("Slave Morality").

Nietzsche was an atheist and harbored a particular disdain for Christianity, which he viewed as playing a key role in supporting Slave Morality. In supporting the Weak and disadvantaged of humanity, Christianity undermined the authority, social position and cultural progress of the Strong. Nietzsche viewed the progress of such Slave Morality as a sort of violation of the natural order and a thwarting of the authentic advancements of civilization available only through the Strong. This view of a "natural order", so typical of 19th-century Europe (e.g., Darwin's Theory of Evolution) is expressed in Nietzsche's principle – Will to Power. Scheler, by comparison, ultimately viewed the universal salvic nature of Christian love as contradicting Nietzsche's assessments, and in later life developed an alternative metaphysical dualism of Vital Urge and Spirit: Vital Urge as closely allied to Will to Power, and Spirit as dependent yet truly distinct in character.

Contrary to Nietzsche's ultimate intent, much of his legacy ultimately led to an implosion of objectivity in which (i) truth became relative to individual perspective, (ii) "might ultimately made right" ("Social Darwinism"), and (iii) ethics would become subjective and solipsistic.

By contrast, Scheler, who also was sceptical over the historically emerging unchecked power of mass culture and the prevalence and leveling power of mediocrity upon ethical standards and upon the individual human person (as a unique sacred value), was nonetheless a theistic ethical objectivist. For Scheler, the phenomenon of Ressentiment principally involved Spirit (as opposed to Will to Power, Drives or Vital Urge), which entailed deeper personal issues involving distortion of the objective realm of values, the self-poisoning of moral character, and personality disorder.