In 1969, a sub-committee of the Astronomy, Space and Radio Board (ASRB) of the Science Research Council was established to examine the SRC’s future support for astronomy in the Northern Hemisphere, with a view to establishing a Northern Hemisphere Observatory (NHO). The proposals for the NHO were considered by a review panel of the ASRB, which ultimately recommended that the RGO should have the prime responsibility for its construction. Site testing began in 1973 and the site chosen was La Palma. The observatory was named the Roque de los Muchachos Observatory (rather than the original title of ‘NHO’) and was ultimately established as a shared facility under an international agreement. It began operating in 1984 and was inaugurated in 1985. The papers in this collection include the deliberations of various committees associated with the project, correspondence between interested parties, including outside contractors, technical reports on instruments, technical drawings, site testing reports, photographs, and information about living conditions on La Palma, as well as the personal files of some key staff members.