Intersex people are those born with any of several sex characteristics, including chromosome patterns, gonads, or genitals that, according to the Office of the United Nations High Commissioner for Human Rights, "do not fit typical binary notions of male or female bodies". The opposite of intersex is endosex, which describes persons born with sex characteristics that are seen as typically male or female at birth.

Sex assignment at birth usually aligns with a child's external genitalia. The number of births with ambiguous genitals is in the range of 1:4,500–1:2,000 (0.02%–0.05%). Other conditions involve the development of atypical chromosomes, gonads, or hormones. The portion of the population that is intersex has been reported differently depending on which definition of intersex is used and which conditions are included. Estimates often range from 0.018% (one in 5,500 births) to 1.7%. The difference centers on whether conditions in which chromosomal sex matches a phenotypic sex which is clearly identifiable as male or female, such as late onset congenital adrenal hyperplasia (1.5 percentage points) and Klinefelter syndrome, should be counted as intersex. Some intersex people choose to identify with a gender different from their assigned sex, though this is not exclusive to intersex people.

Terms used to describe intersex people are contested, and change over time and place. Intersex people were previously referred to as "hermaphrodites" or "congenital eunuchs". In the 19th and 20th centuries, some medical experts devised new nomenclature in an attempt to classify the characteristics that they had observed, the first attempt to create a taxonomic classification system of intersex conditions. Intersex people were categorized as either having "true hermaphroditism", "female pseudohermaphroditism", or "male pseudohermaphroditism". These terms are no longer used, and terms including the word "hermaphrodite" are considered to be misleading, stigmatizing, and scientifically specious in reference to humans. In biology, the term "hermaphrodite" is used to describe an organism that can produce both male and female gametes. Some people with intersex traits use the term "intersex", and some prefer other language. In clinical settings, the term "disorders of sex development" (DSD) has been used since 2006, a shift in language considered controversial since its introduction.

Intersex people face stigmatization and discrimination from birth, or following the discovery of intersex traits at stages of development such as puberty. Intersex people may face infanticide, abandonment, and stigmatization from their families. Globally, some intersex infants and children, such as those with ambiguous outer genitalia, are surgically or hormonally altered to create more socially acceptable sex characteristics. This is considered controversial, with no firm evidence of favorable outcomes. Such treatments may involve sterilization. Adults, including elite female athletes, have also been subjects of such treatment. Increasingly, these issues are considered human rights abuses, with statements from international and national human rights and ethics institutions. Intersex organizations have also issued statements about human rights violations, including the 2013 Malta declaration of the third International Intersex Forum. In 2011, Christiane Völling became the first intersex person known to have successfully sued for damages in a case brought for non-consensual surgical intervention. In April 2015, Malta became the first country to outlaw non-consensual medical interventions to modify sex anatomy, including that of intersex people.