A California unsecured promissory note is a legally binding agreement wherein an individual is not required to furnish collateral before receiving a loan. The agreement will ensure that the borrower repays the loan in full according to the installment plan or deadline indicated on the form. If the lender wishes to add another layer of financial protection, they may require that the borrower select a co-signer who will assume the borrower’s obligations if they fail to deliver payment on time or in full.