Brown hair, also referred to as brunette (when female), is the second-most common human hair color, after black hair. It varies from light to dark brown. It is characterized by higher levels of the dark pigment eumelanin and lower levels of the pale pigment pheomelanin.

Brown hair is common among populations in the Western world, especially among those from Northwestern Europe and the United States, as well as populations in Central Europe, Southeastern Europe, Eastern Europe, Southern Europe, Southern Cone, Brazil, Colombia, Costa Rica, Puerto Rico, and also some populations in the Middle East, Central Asia where it transitions smoothly into black hair. Additionally, brown hair is common among Australian Aboriginals and Melanesians.

The term brunette is the feminine form of the French word brunet, which is a diminutive form of brun meaning "brown/brown-haired", the feminine of which is brune. All of these terms ultimately derive from the Proto-Indo-European root *bhrūn- "brown, grey". The form "brun" (pronounced /bruːn/) is still commonly used in Scotland, particularly in rural areas, and is also the word for "brown" in the Scandinavian languages. In modern English usage, however, it has lost the diminutive meaning and usually refers to any brown-haired girl or woman, or the associated hair color. Merriam-Webster defines "brunet" as "a person having brown hair"—with which they may have "a relatively dark complexion—spelled brunet when used of a boy or man and usually brunette when used of a girl or woman". Although brunet is the masculine version of the popular diminutive form used to describe a little boy or young man with brown hair, the use of "brunet" is uncommon in English. One is more likely to say about a man or boy, "He has brown hair" or "He is brown-haired" than to say, "He is a brunette" (or brunet).

Lighter or darker shades of brown hair may be referred to as "light brunette" or "dark brunette", though in such cases one is generally referring only to the hair color, not using the term as a descriptor for the person; one would be unlikely to say, "She is a light brunette." Rather, one would say, "She has light-brown hair."

Brown-haired individuals predominate in most parts of Europe. In northern and central Europe medium to light brown shades are the most common, while darker shades prevail in the rest of the continent. Brown hair, mostly medium to light brown shades, are also dominant in Australia, Canada, South Africa among White South Africans and the United States among European Americans (from Northern, Central and Eastern Europe), British, Irish, Baltic, Dutch/Flemish, German (including Swiss-German and Austrian), Slovenian, Polish, Ukrainian and Russian people, as well as Southern (Italian, Spanish, Greek, Portuguese) and Southeastern Europe (Bulgarian, Croatian, Serbian).

Similarly to blond hair, brown hair occurs commonly among Australian Aboriginal and Melanesian populations.

Dark brown hair is predominant in the Mediterranean parts of Europe and occasionally in the Middle East, North Africa, Central Asia, and South Asia. Very dark brown hair, easily mistaken for black hair, can be found occasionally in parts of East Asia. This is also true of Southern Cone of South America (Chile, Argentina, Uruguay, Paraguay, central-southern Brazil), Colombia, Andean Region of Venezuela, Costa Rican Central Valley and Puerto Rico.

A study of 1,023 students in Chile found that the most common eye color was brown-black: 71 to 89.4% and the most common hair color was brown from 65.8% to 66.8%.