May determine areas for improvement, inform new products: when to evaluate. Reduce outside influences, distractions methods in a controlled setting; usually for evaluating user interfaces i. e. experiemnets, observation, interviews, Goal: is interface usable by intended user population to carry out tasks for which it was designed for. Investgiates how typical users perform on typical tasks. Tasks performed by user are recorded, logged. Questionnaires, interviews supplement recorded data. Characteristics summary do tasks controlled prototype stage quantitative. Feedback: data via predefined metrics (ex. num errors) Establish the requirements for a new design. Facilitate introduction of technology, or inform deployment of existing technology in new contexts. Goal: unobtrusive, not to affect what users do during evaluation. Data: events, conversations, notes, audio/video recordings. Ex. outdoors, public places, homes: 3. Based on knowledge of usability, users" behavior, context in which the system is to be used, activites users undertake.