a loan agreement is a written contract between two parties — a lender and a borrower — that can be enforced in court if one party does not hold up their end of the bargain. in a loan agreement, a lender can usually also accelerate the loan if the borrower defaults. for example, the bank can start a foreclosure proceeding in a mortgage loan by auctioning off your home and using the proceeds to repay the remaining amount. if the payback terms are complicated, a written agreement allows both parties to clearly spell out any installment payment terms and the exact amount of interest owed. a loan agreement should detail the name of the lender and borrower.