The act of co-signing involves a promise to pay another person's ebt arising out of contract if that person fails to do so. Many realtors and landlords require a cosigner for college students, people with bad credit or people whose income is less than a certain, low multiple of the amount of rent. Other loans typically involving a cosigner are motor vehicle purchase, money loans and mortgages. The statute of frauds existing in most states of the United States requires that any such agreement be in writing and signed by the co-signer in order to be enforceable in a court of law. The legal act or instrument of cosigning is also called a guaranty.