This article discusses the formation of a 'planetary citizenship' based on the 'ecology of knowledges' perspective in Brazilian universities. It is informed by the authors' experiences and the partial results from a research project entitled 'Planetary citizenship and the ecology of knowledges: Interdisciplinarity, transdisciplinarity and internationalization in the university curriculum', a followup project to a previous study conducted with trainee teachers at the Federal University of Ceará (UFC) between 2008 and 2012. Planetary citizenship is conceived here as a floating signifier to be articulated in concrete projects proposed by different groups that work inter- and transdiciplinarily. It is motivated by the major civilizational and humanitarian crisis in which we find ourselves. The ecology of knowledges, premised upon the epistemological diversity of the world, is a dialogue between official/Western knowledge and those other knowledges that have long been excluded from the scenario. It stands within a paradigm shift, a process whereby a new way of perceiving the world comes into existence. We argue that the university is an ideal context for the development of projects that have planetary citizenship as their transdisciplinary theme and the ecology of knowledges as their basic perspective. We illustrate this with examples of this epistemic and pedagogical experimentation, inside and outside the university, that aim to educate planetary citizens.