Waterfall Methodology

Essentially, it's a framework for software development in which development proceeds sequentially through a series of phases. Progress "flows" from one stage to the next, much like the waterfall that gives the model its name.

Stages
1.Project Planning
2. Requirement gathering
3.Design
4.Develop
5.Testing
6.Production
7.Support

Advantages
The waterfall model, as described above, offers numerous advantages for software developers. First, the staged development cycle enforces discipline: every phase has a defined start and end point, and progress can be conclusively identified (through the use of milestones) by both vendor and client. The emphasis on requirements and design before writing a single line of code ensures minimal wastage of time and effort and reduces the risk of schedule slippage, or of customer expectations not being met.
Getting the requirements and design out of the way first also improves quality; it's much easier to catch and correct possible flaws at the design stage than at the testing stage, after all the components have been integrated and tracking down specific errors is more complex. Finally, because the first two phases end in the production of a formal specification, the waterfall model can aid efficient knowledge transfer when team members are dispersed in different locations.
Criticisms
Despite the seemingly obvious advantages, the waterfall model has come in for a fair share of criticism in recent times. The most prominent criticism revolves around the fact that very often, customers don't really know what they want up-front; rather, what they want emerges out of repeated two-way interactions over the course of the project. In this situation, the waterfall model, with its emphasis on up-front requirements capture and design, is seen as somewhat unrealistic and unsuitable for the vagaries of the real