1. Agenda 21: United Nations Conference on the Environment and Development at Rio de Janeiro;Preparatory Committee,1992
2. Agenda 21: Programme of Action for Sustainable Development: the Final Texts of Agreements Negotiated by Governments at the United Nations' Conference on Environment and Development;UNCED,1992
3. Market maturity or Industry maturity;Middleton,1993
4. Sustainable tourism: an evolving global approach;BramwellLane;Journal of Sustainable Tourism,1993