1. Alpenforschungsinstitut gemeninuetzige (1995). Tourismus und Umwelt in Europa: Eine Einfuehrung mit ausgewaehlten europaeischen Tourismusprojekten. Oberammergau: Media Druck und Verlag.
2. An invitation to join. (1998). Green globe. http:/www.wttc.org/WTTCGATE.NSF/0b0eb7cc…22ffdf9e1097802563a6007cfbd4?Open Document (retrieved 18/10/1998).
3. Awards and labels. (1998). EcoNETT http://www.wttc.org/EcoData.nsf/49b6ee51a…ffb6829fc30d002565b5005e1327?oPENdOCUMENT (retrieved 22/11/1998).
4. Managing ecotourism: An opportunity spectrum approach;Boyd;Tourism Management,1996
5. Council Directive of 13 June 1990 on Package Travel, Package Holidays and Package Tours. (1990). Official Journal of the European Communities, 23.6.90. No L 158/59: 59–63.