Child marriage is a formal or an informal union where one or both people are under the age of 18. 

Child marriage is much more likely to happen to girls than to boys. The latest estimates from UNICEF suggest that 19% of women and 3% of men aged 20-24 were married as children. An estimated 640 million women alive today were married before their 18th birthday, compared to 115 million men.

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Worldwide, the figures suggest child marriage is reducing slowly: in the last decade, the rate of child marriage has reduced from 23% to 19%. However, the global data hides the reality for millions of girls. This reduction has happened mostly due to massive decreases in South Asia, where child marriage has dropped from 46% to 26% in the last decade, and also greater decreases in most of the world for wealthier girls compared to poorer girls. 

For girls from the poorest households in sub-Saharan Africa and Latin America, child marriage is increasing. 

Child marriage is a violation of rights and a form of violence against girls (or gender-based violence). Forced child marriage is internationally classified as modern slavery. ​​