A brain drain or human capital flight is a departure of trained and talented individuals for other nations or jurisdictions, due to conflict or lack of opportunity or health hazards where they are living. It parallels the term "capital flight" which refers to financial capital which is no longer invested in the country where its owner lives and earned it. Investment in higher education is lost when the trained individual leaves, usually not to return. Also whatever social capital the individual has been a part of is reduced by their departure.

Historically, the greatest brain drains have been from rural to urban areas. In the 19th century and 20th century there were great migrations to North America from Europe, and in modern times, from developing nations to developed nations. Sometimes such drains occur between developed nations, e.g. from Canada to the United States especially in the finance, software, aerospace, healthcare and entertainment industries due to higher wages and lower taxes.

See also: immigration, instructional capital, brain gain