祖父条款（英文：Grandfather clause），相对于追溯法令，是代表一种允许在旧有建制下已存的事物不受新通过条例约束的特例（“老人老办法，新人新办法。”）。英语中的「祖父」（grandfather）在这场合下会被当作动词或其他衍生形态使用，例如「grandfathered power plant」可能指一座老发电厂未能符合新污染管制条例，但在不溯及既往原则下获得豁免而维持原貌继续运作。

A grandfather clause (or grandfather policy) is a provision in which an old rule continues to apply to some existing situations while a new rule will apply to all future cases. Those exempt from the new rule are said to have grandfather rights or acquired rights. Frequently, the exemption is limited; it may extend for a set time, or it may be lost under certain circumstances. For example, a "grandfathered power plant" might be exempt from new, more restrictive pollution laws, but the exception may be revoked and the new rules would apply if the plant were expanded. Often, such a provision is used as a compromise or out of practicality, to allow new rules to be enacted without upsetting a well-established logistical or political situation. This extends the idea of a rule not being retroactively applied.