A library of free educational videos for ages 3-18. WatchKnowLearn has indexed approximately 50,000 educational videos, placing them into a directory of over 5,000 categories. Users can dive into their innovative directory or search for videos by subject and age level. Video titles, descriptions, age-level information, and ratings are all edited for usefulness. Before clicking through, each video has a preview including the title, host website and creator, a short description, quality and age rating, and views. Classrooms can be created by educators to collect and sort videos for students to watch, including as homework. The Web site invites broad participation in a new kind of wiki system, guided by teachers. WatchKnowLearn itself does not host videos—they serve as a library for links to excellent educational videos that educators have selected.