A satellite state or dependent state is a country that is formally independent in the world but under heavy political, economic, and military influence or control from another country. The term was coined by analogy to planetary objects orbiting a larger object, such as smaller moons revolving around larger planets, and is used mainly to refer to Central and Eastern European countries of the Warsaw Pact during the Cold War, as well as to Mongolia and Tuva between 1924 and 1990, all of which were economically, culturally, and politically dominated by the Soviet Union. While primarily referring to the Soviet-controlled states in the Central and Eastern Europe or Asia, in some contexts the term also refers to other countries under the Soviet hegemony during the Cold War, such as North Korea (especially in the years surrounding the Korean War of 1950–1953), Cuba (particularly after it joined the Comecon in 1972), North Vietnam during Vietnam War, and to some countries in the American sphere of influence, such as South Vietnam (particularly during the Vietnam War). In Western usage, the term has seldom been applied to states other than those in the Soviet orbit. In Soviet usage, the term applied to the states in the orbit of Nazi Germany, Fascist Italy, and Imperial Japan, whereas in the West the term to refer to those has typically been client states.

The Oxford English Dictionary traces the phrase satellite state in English back as early as 1916.

In times of war or political tension, satellite states sometimes serve as buffers between an enemy country and the nation exerting control over the satellites.