宗主权是指国家对其属国的内政及外交拥有干预的权力，对属国享有宗主权的国家即是宗主国。宗主国通常在一定程度上拥有属国的外交权，但属国仍保有独立的自治权力。较有权的一方为宗主。英文里的宗主权「Suzerainty」原是用来形容奥图曼帝国及其周围属地的关系。与主权不同的是，宗主关系里的附庸通常有一定程度的自治权，也可指封建帝王对进贡诸侯的关系。

宗主在历史上许多帝国中存在，但很难用20世纪后的国际法定义，因为宗主关系需要很明确的存在或不存在。一个主权独立的国家可以和一个强权签署协约受其保护，但现代国际法并没有硬性规定宗主关系不能撤回。

Suzerainty (/ˈsjuːzərənti/ or /ˈsjuːzərɛnti/) is a situation in which a powerful region or people controls the foreign policy and international relations of a tributary vassal state while allowing the subservient nation internal autonomy. The dominant entity in the suzerainty relationship, or the more powerful entity itself, is called a suzerain. The term suzerainty was originally used to refer to the relationship between the Ottoman Empire and its surrounding regions. It differs from sovereignty in that the tributary enjoys some (often limited) self-rule.