User-centered design is a multidisciplinary approach to creating products, services, and systems by grounding decisions in the needs, behaviors, and constraints of intended users. In user-centered design practice, teams iterate through research, ideation, prototyping, and usability evaluation to reduce risk and improve task success. The approach is formalized in ISO 9241-210, which outlines principles such as understanding context of use, involving users throughout, and evaluating designs against requirements. Common methods include interviews, contextual inquiry, diary studies, surveys, card sorting, and moderated or unmoderated usability testing; outputs often include personas, journey maps, task flows, and service blueprints. Metrics such as task completion rate, time on task, error rate, System Usability Scale (SUS), and Net Promoter Score are frequently reported; guidance is widely disseminated by the Nielsen Norman Group and Usability.gov. Accessibility is an integral concern, with practitioners referencing the W3C Web Content Accessibility Guidelines and inclusive research practices. The approach is applied across software, healthcare, civic services, and hardware, and is complementary to agile and lean development by informing backlogs with validated user insights.

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