國家間「自由聯合（free association）」關係，通常指一個較大的國家，透過條約與另一個相對較小的國家建立起聯繫關係，通常由較小國家授權較大國家，為其提供在國防或在外交方面之專屬權利；而較小國家可從較大國家手中取得財政經濟方面的資助，這樣的聯繫關係並非是保護國與被保護國之間的關係，而是在國際關係上保持一個特殊國與國安排。自由聯合國家在國際法上並非僅具有實體（entity）之法律地位，而是一個完整的、獨立的國際法人，享有國際法主體之權利與義務，自願地與他國締結協定，將相關權利授權予另一國。本文首先透過自由聯合關係發展背景與過程進行簡要概述，其後就外交與防務制度安排進行說明，同時以美國及紐西蘭各自發展的兩種模式進行比較，藉此深入瞭解另一類的特殊國與國關係安排。

The relationship of free association between states usually refers to a larger country that establishes certain bond of association with a relatively small country. In this case, it's generally for a small state to authorize the larger state to provide exclusive rights on the aspect of national security or diplomatic relation; in return, the small state can acquire a significant financial and economic support from the larger state. This kind of association is not a protectorate relationship; instead, it is a special arrangement for two nations for the foreign relations. A state of free association is not merely an entity under international law, rather, it possesses complete and independent status and can be a subject of international law which voluntarily give up certain sovereign right to the other for the return of another. This article will briefly introduce the background and progressive development of the relation of free association in advance. Then the article will focus on the arrangement concerning the right of diplomatic relation and defense and at the same time make some analogies in comparing the developing modes of USA and New Zealand in order for the author to further understand the special arrangement for a state-via-state relationship.