In this chapter, we critically review definitions and operationalizations of the eco tourist and investigate whether the operationalizations used in empirical studies match the theoretical definitions. Results indicate that both definitions and operationalizations differ substantially across studies and that operationalizations used in empirical studies frequently are not in line with the definitions specified by the same authors. Therefore, there is currently no common understanding of who the eco tourist really is. This lack of common understanding appears to be due to different positions taken with respect to two key criteria: the eco tourist’s interest in nature and their level of environmental sustainability. We propose a simple naming convention that provides clear guidelines for future researchers with respect to both the definition and the operationalization of eco tourists. In 2008, Dolnicar, Crouch and Long asked the question how much we actually know about tourists who behave in an environmentally friendly way, concluding that ‘operationalisations of EFTs [environmentally friendly tourists] are inconsistent and, at times, do not ensure that EFTs are actually studied, thus jeopardizing the quality of cumulative knowledge on this critical issue.