An agreement in principle, also known as a “decision in principle,” “promise of mortgages,” or “mortgage in principle,” is a certificate or statement from a lender that states that they would lend you a certain amount “in principle.” You don`t need to get an agreement in principle, but it can sometimes help when you`re looking for a home (see “How an AIP can help,” below). Real estate agents will often want to make sure you`ll be able to get a mortgage on a property before making an offer, so it can be helpful to have an agreement by that date. This type of agreement is acceptable if you think it is not set in stone until the final agreement is signed. It`s a bit like those so-called approved credit card offers that you receive in the mail and then send the application that tells you it`s denied. It`s frustrating, really.