The commander-in-chief is the person who holds supreme authority over a country's military forces. In many nations, this role belongs to the head of state such as a president, prime minister, or monarch. In the United States, for example, the president serves as commander-in-chief, meaning all major military decisions ultimately require the president's approval.

This arrangement reflects an important idea called civilian control of the military: the belief that elected or appointed leaders, rather than military officers alone, should have final authority over armed forces. The title can also apply more specifically. A general might be commander-in-chief of forces in a particular region, commanding all military units there.

Being commander-in-chief carries tremendous responsibility, because military decisions can affect the safety and lives of millions of people.