Agile is flexible and works in short cycles, so the team can build part of the project, get feedback, and make changes as they go. It is useful when requirements may change or when the customer is not completely sure what they want at the start.

A Plan and Document, or Waterfall, process is more structured. The team tries to define all requirements, design, and documentation before building the system. Each phase is usually completed before the next one begins, so changes later in the project can be harder and more expensive.

The biggest difference is how each process handles change. Agile expects change and uses feedback throughout development, while Waterfall tries to avoid change by planning carefully upfront. Agile often has more customer involvement during the project, while Waterfall usually relies on detailed documents and approvals at major stages.