The days of a handshake and a promise are long gone. A contract is crucial to any business arrangement. Both parties come to an understanding about what they will be providing and what they will be receiving in this contract and what each parties rights are according to this contract. Any changes or amendments to that contract should be put in writing as well.
If you don’t currently use a contract you can find many examples on line and at an office supply store. I recommend having your attorney review your contract to be sure that the contract is clear and that you and your business is protected by this contract.