A buffer state is a country lying between two rival or potentially hostile greater powers that by its sheer existence is thought to prevent conflict between them. Buffer states typically pursue a neutralist foreign policy, which distinguish them from satellite states.

Examples of buffer states include:

• Afghanistan, between Russia and British India
• Mongolia, between the People's Republic of China and the Soviet Union, now Russia
• Poland following World War I, located between Germany and the Soviet Union
• North Korea during and after the Cold War, whom some analysts see as a buffer state between the military forces of the People's Republic of China and American forces in South Korea
• Belgium before World War I, serving as a buffer between the United Kingdom, France, and Germany

The invasion of a buffer state by one of the powers surrounding it will often result in war between the powers.