Iterative design is a design methodology that involves a cyclic process of prototyping, testing, analyzing, and refining a product or process. The process is intended to improve the quality and functionality of a design by making changes and refinements based on the results of testing the most recent iteration of a design. In iterative design, interaction with the designed system is used as a form of research for informing and evolving a project, as successive versions, or iterations of a design are implemented.

Iterative design is used in many fields, including software applications, engineering, design, marketing, and education. The iterative design process allows designers to create, test, analyze, and refine ideas quickly during any phase of the design process. By focusing on how users think and behave, iterative design helps design teams reduce usability issues, especially in the early stages of a project when the cost of eliminating mistakes is modest.

The iterative design process can differ from methodology to methodology, but can generally be summarized into five distinct stages:

1. Research: This stage involves gathering information about the problem, the users, and the context in which the product will be used.
2. Ideation: This stage involves generating ideas for the product based on the research conducted in the previous stage.
3. Prototyping: This stage involves creating a prototype of the product based on the ideas generated in the previous stage.
4. Testing: This stage involves testing the prototype with users to identify any usability issues or areas for improvement.
5. Refinement: This stage involves making changes and refinements to the prototype based on the results of testing, and then repeating the process from the ideation stage.

Iterative design is a way of confronting the reality of unpredictable user needs and behaviors that can lead to sweeping and fundamental changes in a design. User testing will often show that even carefully evaluated ideas will be inadequate when confronted with a user test. Thus, it is important that the flexibility of the iterative designs implementation approach extends as far into the system as possible. Designers must further recognize that user testing results may suggest radical change that requires the designers to be prepared to completely abandon old ideas in favor of new ideas that are more equipped to suit user needs.