In international relations reciprocity is the principle by which a State grants benefits and rights to another State, only if the other State grants the same treatment.

This principle is adopted by States when entering into agreements and treaties so that, in addition to the reciprocity of favours and treatments, uniform conduct, fulfilment of international obligations and application of the rule quid pro quo (from the Latin: this for that) are guaranteed.

The principle of reciprocity is not adopted for humanitarian law and human rights treaties, for which contracting States, in agreement with the humanitarian reasons governing such treaties, are obliged to abide by such principles even in relations with States that fail to respect them.