保护国又称保护领、受保护国、被保护国、受保护领地，是受较强之国家（宗主国）支配和保护的国家或地区，是殖民地形式的一种。

保护国是非独立国的一种，也是殖民统治的一种特殊形式。帝国主义国家为了掠夺原材料产地和国际市场，用强力的手段迫使弱小国家，落后国家同他签不平等条约，以“保护”为名，控制和吞并弱小国家。这些弱小国家就称为保护国。宗主国与保护国之关系为国家之间的不平等关系之一，弱势国家因签订不平等条约而接受强势国家的军事保护，以致无法自理内政、外交事务，甚至丧失主权。

如果被保护的对象为民族实体、共同体，或通过征服从别国瓜分土地，此类常被称为保护地、领地、境外领土。此类常在国际法中主权性质发生变化，演变为国家的领土主权范畴，各国对此称谓不尽一致。保护国或保护地或属地多属于殖民地。随着第二次世界大战的结束、联合国的成立以及民族独立运动的发展，国家之间的保护国关系渐渐消失。

A protectorate, in its inception adopted by modern international law, is a dependent territory that has been granted local autonomy and some independence while still retaining the suzerainty of a greater sovereign state. In exchange for this, the protectorate usually accepts specified obligations, which may vary greatly, depending on the real nature of their relationship. Therefore, a protectorate remains an autonomous part of a sovereign state. They are different from colonies as they have local rulers and people ruling over the territory and experience rare cases of immigration of settlers from the country it has suzerainty of. However, a state which remains under the protection of another state but still retains independence is known as a protected state and is different from protectorates.