The National Science Foundation provides explicit links from its website under several circumstances:

• From its "related sites" page: These links are limited to major federally-funded science centers and laboratories, other federal science-funding agencies, other national science foundations, and selected major U.S. and international science organizations.
• To selected organizations and agencies as a convenience to NSF web customers. Examples include links to the web pages maintained by Research Experiences for Undergraduates (REU) sites; and links to other federal agencies jointly supporting research programs with the National Science Foundation.

Questions concerning whether a link is appropriate from the NSF web to an NSF-funded project, center, or research site, should in most cases be referred to the appropriate Program Manager, who can redirect the request if necessary to their Directorate webmaster or to the NSF webmaster.