Nihilism (; from Latin nihil 'nothing') is a philosophy, or family of views within philosophy, that rejects generally accepted or fundamental aspects of human existence, such as objective truth, knowledge, morality, values, or meaning. The term was popularized by Ivan Turgenev, and more specifically by his character Bazarov in the novel Fathers and Sons.

There have been different nihilist positions, including that human values are baseless, that life is meaningless, that knowledge is impossible, or that some set of entities do not exist or are meaningless or pointless.

Scholars of nihilism may regard it as merely a label that has been applied to various separate philosophies, or as a distinct historical concept arising out of nominalism, skepticism, and philosophical pessimism, as well as possibly out of Christianity itself. Contemporary understanding of the idea stems largely from the Nietzschean 'crisis of nihilism', from which derive the two central concepts: the destruction of higher values and the opposition to the affirmation of life. Earlier forms of nihilism, however, may be more selective in negating specific hegemonies of social, moral, political and aesthetic thought.

The term is sometimes used in association with anomie to explain the general mood of despair at a perceived pointlessness of existence or arbitrariness of human principles and social institutions. Nihilism has also been described as conspicuous in or constitutive of certain historical periods. For example, Jean Baudrillard and others have characterized postmodernity as a nihilistic epoch or mode of thought. Likewise, some theologians and religious figures have stated that postmodernity and many aspects of modernity represent nihilism by a negation of religious principles. Nihilism has, however, been widely ascribed to both religious and irreligious viewpoints.

In popular use, the term commonly refers to forms of existential nihilism, according to which life is without intrinsic value, meaning, or purpose. Other prominent positions within nihilism include the rejection of all normative and ethical views (§ Moral nihilism), the rejection of all social and political institutions (§ Political nihilism), the stance that no knowledge can or does exist (§ Epistemological nihilism), and a number of metaphysical positions, which assert that non-abstract objects do not exist (§ Metaphysical nihilism), that composite objects do not exist (§ Mereological nihilism), or even that life itself does not exist.