A person who is neither a promisor nor promisee in a contractual agreement, but stands to benefit from the contract’s performance. A third-party beneficiary may legally enforce that contract, but only after his or her rights have already been vested (either by the contracting parties’ assent or by justifiable reliance on the promise).
According to the Restatement (First) of Contracts § 133 (1932), there are three classes of third-party beneficiaries:
"(a) a donee beneficiary if it appears from the terms of the promise in view of the accompanying circumstances that the promise of the promisee in obtaining the promise of all or part of the performance thereof is to make a gift to the beneficiary or to confer upon him a right against the promisor to some performance neither due nor supposed or asserted to be due from the promisee to the beneficiary;
"(b) a creditor beneficiary if no purpose to make a gift appears from the terms of the promise in view of the accompanying circumstances and performance of the promise will satisfy an actual or supposed or asserted duty of the promisee to the beneficiary, or a right of the beneficiary against the promisee which has been barred by the Statute of Limitations or by a discharge in bankruptcy, or which is unenforceable because of the Statute of Frauds;
"(c) an incidental beneficiary if neither the facts stated in Clause (a) nor those stated in Clause (b) exist."