3 Exceptions to the Rule on Prescription of Actions
An action prescribes by the lapse of time fixed in the Civil Code (Articles 1139 to 1155).
 Prescription and estoppel cannot be invoked against the State. In any case, even granting that the said official was negligent, the doctrine of estoppel cannot operate against the State . "It is a well-settled rule in our jurisdiction that the Republic or its government is usually not estopped by mistake or error on the part of its officials or agents. Consequently, the State may still seek the cancellation of the title issued to Perpetuo Alpuerto and his successors-interest pursuant to Section 101 of the Public Land Act. Such title has not become indefeasible, for prescription cannot be invoked against the State. (G.R. No. 182913; November 20, 2013)
 Even if the defense of prescription has not been raised in a motion to dismiss or an answer, if the plaintiff’s complaint or evidence shows that the action had prescribed, the action shall be dismissed by the court. (Section 1of Rule 9)
 Prescription cannot be invoked as a ground if the contract is alleged to be void ab initio but where prescription depends on whether contract is void or voidable, there must be a hearing. Necessarily, petitioners' contention that the action has prescribed cannot be sustained. Prescription cannot be invoked as a ground if the contract is alleged to be void ab initio. It is axiomatic that the action or defense for the declaration of nullity of a contract does not prescribe. (G.R. No. 131889; March 12, 2001)