A written guaranty from a third party guarantor (usually a bank or an insurance company) submitted to a principal (client or customer) by a contractor (bidder) with a bid.

A bid bond ensures that on acceptance of a bid by the customer the contractor will proceed with the contract and will replace the bid bond with a performance bond. Otherwise, the guarantor will pay the customer the difference between the contractor's bid and the next highest bidder. This difference is called liquidated damages, which cannot exceed the amount of the bid bond. Unlike a fidelity bond, a bid bond is not an insurance policy, and (if cashed by the principal) the payment amount is recovered by the guarantor from the contractor.

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