A prototype, or sometimes called a “spike” if it’s limited in scope or functionality, is a technique used by agile teams to create a product or service proof-of-concept in order to quickly solicit feedback about the design from customers and end users, or to help the team understand the user stories (see “Spike (Design Spike) for more information). Prototypes or spikes can be developed in various ways depending on the type of feedback desired. For example, they can be created using basic materials (e.g., pen and paper) or sophisticated technologies (e.g., markup languages). Prototypes or spikes allow customers to interact with a product giving product teams insight into which features are most important to the end user. The ability to experiment with multiple prototype iterations, and test various concepts in the field, provides critical input into refining the product vision.