Background/Question/Methods: Over the last two decades, the definition of ecological literacy has developed and matured, just as the science of ecology has evolved. Recent definitions of ecological literacy include understanding key ecological systems, using sound ecological thinking, and also understanding the nature of ecological science and its interface with society. More specifically, recent work suggests that ecologically literate people have the ability to use ecological understanding, thinking and habits of mind for living in, enjoying, and /or studying the environment. Today, different types of literacies have emerged, including scientific (in its broadest sense), artistic, mathematical, technological, environmental, language, and many more. Indeed it may seem that every field has a literacy movement. Interestingly, until the late 1800s, there was no word ‘literacy,' and in the Oxford Dictionary, ‘illiteracy' predates ‘literacy' by several hundred years. Historically, illiteracy referred to the inability to read or write, and likewise, literacy, in its historical and most simple definition, referred to the ability to read and write. Beyond the recent numerous (and sometimes complex) theoretical and practical meanings, today we have moved beyond the old binary distinction of illiterate versus literate to embrace literacy as a continuum from zero to advanced skills. Moreover, there is an added context that considers the functional, cultural, and critical dimensions of literacy. Results/Conclusions: Recognizing that we cannot teach everyone the whole discipline of ecology and the other environmental sciences, what is the shorter list of “essential things” people need to understand about ecological systems to be ecologically literate? To answer this question, we briefly explore the theoretical evolution of the concept of literacy, and the theoretical and practical evolution of environmental and ecological literacies, in particular. Next, we consider the notion of literacy and trace the history of the practical development of the essential knowledge, skills, and values components of these literacies within environmental and ecology education. Finally, we propose a context for discussing what it might mean to be functionally, culturally, and critically ecologically literate, and how ecological literacy fits within the broader notion of environmental citizenship.