合同的相对性是指有效成立的合同仅仅对通过意思表示接受合同约束的合同双方有约束力，而对合同第三人一般没有约束力。一般认为，合同相对性起源于罗马法中的债的相对性，在罗马法中，债（obligation）这个词，有时也称为“法锁”（juris vinelum）。所谓法锁或法律上的锁链，即指债的关系是债权人和债务人之间的法律关系，而不涉及特定的当事人之外的第三人。相比较于作为对世权的物权，债权也被称之为‘对人权’。 合同相对性也是作为现代民法基石的意思自治原则的具体体现。

The doctrine of privity in the common law of contract provides that a contract cannot confer rights or impose obligations arising under it on any person or agent except the parties to it.

The premise is that only parties to contracts should be able to sue to enforce their rights or claim damages as such. However, the doctrine has proven problematic due to its implications upon contracts made for the benefit of third parties who are unable to enforce the obligations of the contracting parties.