The Waterfall model was one of the very first of the development methodologies to be introduced. It is the methodology of choice when the customer wants a fixed price and timeline and prefers not to use Agile. With the Waterfall approach the project is divided into a number of sequential phases and each phase is completed fully before the following phase can begin. This methodology is most commonly used for the larger projects where the requirements are fully understood, documented, and signed-off. A review takes place at the end of each phase, to determine if the project is on track.