National Science Digital LibraryThe National Science Digital Library provides high quality online educational resources for teaching and learning, with current emphasis on the sciences, technology, engineering, and mathematics (STEM) disciplines—both formal and informal, institutional and individual, in local, state, national, and international educational settings. NSDL does not hold content directly—instead, we provide structured descriptive information (metadata) about web-based educational resources held on other sites by their providers, who contribute this metadata to NSDL for organized search and open access to educational resources via NSDL.org and its services.