A contract statement of work is an input/output device that refers to a narrative description of the products, results, and services that are expected to be delivered at the conclusion of a contract. The contract statement of work will typically be developed at the start of the project and serves to encompass the entirety of the deliverables. This can serve a number of important purposes. First, it makes sure that all parties are on the same page. That all parties are expecting the same deliverables, of the same quality, delivered at the same time. It results in fewer surprises when it comes time for the seller to deliver his final deliverables, and for the buyer to make his final payment. Secondly, the contract statement of work provides a sound basis for discussion in the event a deliverable is not delivered according to satisfaction. The contract statement of work should provide all parties with a good starting point in the event any modifications need to be made.
This term is defined in the 3rd edition of the PMBOK but not in the 4th.