A Buy-Sell Agreement is an integral part of any business plan. While business partners anticipate being in business together well into the future, this is not always the case. A Buy-Sell Agreement sets out the terms and conditions for the transfer of ownership of the business in the event of death, disability, retirement or disagreement. The agreement should include a formula or process for calculating the fair market value of the business in order to simplify the buy-out of an owner.