A co-signer is a person who signs an agreement to pay off a loan for someone else if that someone else defaults. Co-signing is a technique often used among family and friends to allow a person with good credit to vouch for a person with new credit or bad credit to get a loan. The presence of a co-signer makes lenders more willing to approve loans for high-risk borrowers. While co-signing allows the person with bad credit to get a loan, it puts the person with good credit on the hook for the entire amount borrowed. CreditCards.com polling data shows that 4 in 10 co-signers end up paying at least part of the debt.