The background of this essay is based upon my high interest for the phenomenon ecotourism and its importance for a sustainable development in the LDCs, and my future research in Guatemala. The purpose of this paper has been to study and describe the phenomenon ecotourism, to analyse the consequenses of the outcome of ecotourism in less developed countries, and also to disentangle how the concept should be sustainably implemented in these countries. The method has been concentrated to literature studies with a deductive approach. I begin with describing the concept ecotourism and its definitions, criteria and principles and their importance for development. Next, spatial impacts of the world such as deforestation and desertification and also the economic, socio-cultural and ecological impacts of tourism will be analysed. Thereafter, the impacts of ecotourism will be studies and analysed. To explore further how ecotourism may be developed in the best sustainable way in the LDCs, planning, development and management through strategies and frameworks have been disentangled. These theoretical issues have next been shown how to be implemented in practice in three countries such as, Costa Rica, Nepal and Kenya. I round off with discussing these mentioned issues and establish the fact that ecotourism can minimize environmental costs and maximize economic benefits, if it is planned and managed in an appropriate and correct way. The process of development must be looked upon as a long-term procedure and every level involved in it has to cooperate. Education is an important element in ecotourism, which should include information and interpretation of the visitors as well as the operators, guides and others involved in the activity.