# Waterfall Methodology > **Waterfall** is a traditional methodology in which tasks and phases are > completed in a **linear**, **sequential** manner, and each stage of the > project must be completed before the next begins. The project manager is > responsible for prioritizing and assigning tasks to team members. In > Waterfall, the criteria used to measure quality is clearly defined at the > beginning of the project. - Adopt waterfall when - There are tasks to complete before another can begin - Phases of the project are clearly defined - Project changes are expensive to implement once it's started