In the field of international relations, a client state, is a state that is economically, politically, and militarily subordinated to a more powerful controlling state. Alternative terms for a client state are satellite state, associated state, and dominion, condominium, self-governing colony, and neo-colony, protectorate, vassal state, puppet state, and tributary state.

A tributary state is a pre-modern state in a particular type of subordinate relationship to a more powerful state which involved the sending of a regular token of submission, or tribute, to the superior power. This token often took the form of a substantial transfer of wealth, such as the delivery of gold, produce, or slaves, so that tribute might best be seen as the payment of protection money. It might also be more symbolic: sometimes it amounted to no more than the delivery of a mark of submission such as the bunga mas that rulers in the Malay Peninsula used to send to the kings of Siam, or the Tribute of the Maltese Falcon that the Grand Master of the Order of St. John used to send annually to the Viceroy of Sicily in order to rule Malta. It might also involve attendance by the subordinate ruler at the court of the hegemon in order to make a public show of submission.