Human height is dependent according to both nature and nurture. The particular human genome that an individual inherits is a large part of the first variable (nature) and a combination of health and environmental factors present before adulthood (when growth stops) are a major part of the second determinant ("nurture"). Hereditary factors include both genes and chromosomes, and are inborn. Environmental factors are events that occur before adult height is reached, such as diet, exercise, and living conditions.

When populations share genetic background and environmental factors, average height is frequently characteristic within the group. Exceptional height variation (around 20% deviation from average) within such a population is usually due to gigantism or dwarfism; which are medical conditions due to specific genes or to endocrine abnormalities. In regions of extreme poverty or prolonged warfare, environmental factors like malnutrition during childhood and/or adolescence may account for marked reductions in adult stature even without the presence of any of these medical conditions. This is one reason that immigrant populations from regions of extreme poverty to regions of plenty may show a decrease in stature, despite sharing the same gene pool.

The average height for each sex within a population is significantly different, with adult males being (on average) taller than adult females. Women ordinarily reach their greatest height at a younger age than men. Vertical growth stops when the long bones stop lengthening, which occurs with the closure of epiphyseal plates. These plates are bone growth centers that disappear ("close") under the hormonal surges brought about by the completion of puberty. Puberty generally occurs several years earlier in young women than in young men, and so final adult height is reached earlier in women. Adult height for one sex in a particular ethnic group follows more or less a normal distribution.

Adult height between ethnic groups often differs significantly, as presented in detail in the chart below. For example, the average height of women from the Czech Republic is currently greater than that of men from Malawi. This may be due to genetic differences, to childhood lifestyle differences (nutrition, sleep patterns, physical labor) or to both.

At 2.57 metres (8 ft 5.5 in), Leonid Stadnyk, of Zhytomyr Oblast, Ukraine, is believed to be the world's tallest living man, although his height is disputed because of his refusal to be measured. The current proven tallest man is Bao Xishun at 2.36 meters (7 feet 9 inches). The tallest man in modern history was Robert Pershing Wadlow from Illinois in the United States, who was born in 1918 and stood 2.72 m (8 ft 11.1 inches) at the time of his death in 1940.

The maximal height that an individual attains in adulthood is not maintained throughout life if that life is a very long one. Again, depending on gender (male v. female), genetic, and environmental factors, there is shrinkage of stature that may begin in middle age in some individuals but is universal in the extremely aged. This decrease in height is due to such factors as decreased height of inter-vertebral discs because of desiccation, atrophy of soft tissues, and postural changes secondary to degenerative disease.