1. Armstrong, E.K., and B. Weiler. 2002. Getting the message across: An analysis of messages delivered by tour operators in protected areas. Journal of Ecotourism 1(2): 104–121.
2. Berno, T., and K. Bricker. 2001. Sustainable tourism development: The long road from theory to practice. International Journal of Economic Development 3(3): 1–18.
3. Black, R.S. 2015. Codes of conduct. In Encyclopaedia of sustainable tourism, ed. B. Garrod and C. Cater. Wallingford: CABI Publishing.
4. Black, R., and B. Weiler. 2005. Quality assurance and regulatory mechanisms in the tour guiding industry: A systematic review. Journal of Tourism Studies 16(1): 24–37.
5. Budenau, A. 2005. Impacts and responsibilities for sustainable tourism: A tour operator’s perspective. Journal of Cleaner Production 13: 89–97.