A guarantee is a promise to ensure that a third party fulfils its obligations and/or a promise to fulfil those obligations if that third party fails to do so. It is a contractual agreement that creates a secondary obligation to support a primary obligation of one party to another. For example, the secondary obligation may be to repay a loan made by a lender to a borrower. If that lender has doubts about the borrower’s ability to perform its primary obligation it may seek a guarantee.