In order to be a valid and enforceable contract, an agreement to purchase real property must be in writing and need only describe the property generally, contain the terms of sale, provide for a specific closing date and be signed by both buyer and seller. This agreement is the most important document in the entire transaction. In many cases, buyers and sellers execute these agreements without the aid of attorneys, using forms provided by real estate brokers. Where a party executes a contract before consulting with an attorney, it is generally beyond the attorney's power to change or modify the terms of the contract except by mutual consent of the parties. Therefore, whenever possible, it is desirable to consult with an attorney prior to entering into any contract.

Among the items to be negotiated in a purchase and sale contract, in addition to the price, are the type of mortgage the buyers will need as a condition of purchasing and how long they will have to obtain a commitment from a lender to provide such a mortgage. Other items include date of occupancy, the type and effect of inspections to be done, and the responsibility for loss in the event of catastrophic damage to the property.