Ecotourism is responsible travel to natural areas that educates and inspires through interpretation—increasingly paired with practical action—that helps conserve the environment and sustain the well-being of local people. Ecotourism is the fastest-growing segment of the travel and tourism industry, and its economic value is projected to exceed USD$100 billion by 2027. Ecotourism emerged in the 1960s as a response to the destructive effects of mass tourism and has been embraced by an increasing number of governments, especially in the developing world, as a vehicle for achieving the UN Sustainable Development Goals. As an emerging, interdisciplinary field of study, ecotourism has reached a critical inflection point, as scholars reflect on the achievements and shortcomings of several decades of research and set out the research agenda for decades to come. The field has yet to achieve consensus on the most basic questions, such as how ecotourism is, or should be, defined; what makes it different from nature-based and related forms of tourism; and what factors ultimately determine the success or failure of ecotourism as a vehicle for sustainable development. This lack of consensus stems in part from the different perspectives and agendas within and between the academic, policy, and industry communities. Because it is based on measured and observed phenomena, empirical research has a critical role to play in advancing the theory and practice of ecotourism. However, scholars also recognize that to fulfill this role, methodologies must evolve to become more longitudinal, scalable, inclusive, integrative, and actionable.