Contemporary religious communication is characterized by semantic variations that attempt to integrate new topics and concerns originating in non-religious discourses while still claiming to convey the same religious "truth" or eternally valid view of reality. This development results in new semantics or forms of the religious symbol system. For example, the appropriation of bioethical and ecological semantics by religious individuals and organizations and their engagement in environmental enterprises produces an "eco-religious communication" that intends to be religious and ecological at the same time. The study of these phenomena will have to identify contextual factors that contribute to or directly cause semantic transformations in the religious system, and, in addition, discern the structures and processes that guide the selection and repeated use of new semantics by the system. This paper attempts to discuss these semantic transformations in terms of system/environment relations, and to clarify the internal conditions for the development of eco-religious communication. The paper first mentions an example of eco-religious communication in a Christian context that refers to the concept of "sustainability", before introducing basic concepts of Niklas Luhmann's approach to the Sociology of Knowledge that are relevant to the study of eco-religious phenomena, and finally explaining the conditions for the translation process that results in eco-religious semantics.