We are fortunate to be living in one of the most exciting times in the history of symbiosis research: a true renaissance period in which ecological and evolutionary theory, organismal knowledge, and the dual powers of technology and computational biology are framing a new understanding of symbiotic interactions. From studies of diffuse coevolution and horizontal transmission to context- dependency, the -omics of interactions, and new evidence of nested symbioses, recent work is revisiting — and sometimes rewriting — the rules for how we think about 'the living together of unlike organisms.' In this presentation I will focus on one of earth's most prevalent symbioses -- the association of endophytic fungi with photosynthetic organisms -- to highlight (1) recent findings regarding ecological interactions at levels from leaves to landscapes; (2) new insights into mechanisms underlying plant-fungal associations from local to global scales; and (3) emergent questions, which together speak to the challenge, excitement, and promise that engage us across disciplines and organisms in the broader study of symbiosis.