Mainstream approaches ecotourism focus on the main idea that the tourism activities employ the kinds of sustainability that are economically viable, ecologically maintainable and socially equitable. Hence, ecotourism is considered a special type of sustainable tourism that aims at responsible use of natural, cultural and historical resources, and it simultaneously contributes to the local and national development and the protection of natural areas. This paper presents critical assessment of the mainstream explanations about the nature of ecotourism. To do so, the critical views in the related literature are collected, reviewed and presented. Their criticisms include the central assumptions and explanations provided by the mainstream scholars about ecotourism, such as definition, goals and outcomes of ecotourism, business practices, environmental sustainability, ethics and tourism policy. It is clear that critical approaches come up with explanations that are diametrically different and, thus reject the validity of the mainstream approaches.