Nudity is the state of being in which a human is without clothing.

The loss of body hair was one of the physical characteristics that marked the biological evolution of modern humans from their hominin ancestors. Adaptations related to hairlessness contributed to the increase in brain size, bipedalism, and the variation in human skin color. While estimates vary, for at least 90,000 years anatomically modern humans were naked. The invention of clothing was part of the transition to being not only anatomically but behaviorally modern.

With the rise of civilizations, clothing became part of non-verbal communications, indicating a person's social status and individuality, thus the lack of clothing could be a sign of low status. However, through much of history until the late modern period, people might be unclothed by necessity or convenience when engaged in labor and athletics; or when bathing or swimming. Such functional nudity occurred in groups that were usually but not always segregated by sex.

In ancient religions, deities were often depicted as perfect naked humans. Indigenous peoples in tropical climates used clothing for decorative or ceremonial purposes but were often nude, having neither the need to protect the body from the elements nor any concept of sexual shame. The association between nudity and shame is unique to followers of Abrahamic religions. The spread of Western concepts of modest dress was part of colonialism.

Social norms regarding nudity vary widely, reflecting cultural ambiguity towards the body and sexuality, and differing conceptions of what constitutes public versus private spaces. Norms relating to nudity are different for men than they are for women. In many societies, both ancient and contemporary, children might be naked until the beginning of puberty. Individuals may intentionally violate norms relating to nudity; those without power may use nudity as a form of protest, and those with power may impose nakedness on others as a form of punishment.

While the majority of societies require clothing in most situations, others recognize non-sexual nudity as being appropriate for some recreational, social or celebratory activities, and appreciate nudity in the arts as representing positive values. Societies such as Japan and Finland maintain traditions of communal nudity based upon the use of baths and saunas that provided alternatives to sexualization. Some societies and groups continue to disapprove of nudity not only in public but also in private based upon religious beliefs. Norms are codified to varying degrees by laws defining proper dress and indecent exposure.