Protection of existing and potential observatory sites: Triennial report 2009-2012 of IAU Commission 50

(abridged) The activities of the Commission have continued to focus on controlling unwanted light and radio emissions at observatory sites, monitoring of conditions at observatory sites, and education and outreach. Commission members have been active in securing new legislation in several locations to further the protection of observatory sites as well as in the international regulation of the use of the radio spectrum and the protection of radio astronomical observations. In 2009, at its XXVII General Assembly in Rio de Janeiro, the IAU passed Resolution B5 in Defence of the Night Sky and the Right to Starlight. The Resolution encourages IAU members to assist in raising public awareness about the contents and objectives of the International Conference in Defence of the Quality of the Night Sky and the Right to Observe Stars [http://www.starlight2007.net/], in particular the importance of preserving access to an unpolluted night sky for all mankind.