Corals associate with diverse eukaryotic (endosymbiotic dinoflagellates of the genus Symbiodinium, other protists, fungi, endolithic algae), prokaryotic (Bacteria, Archaea), and acellular (viruses) microbiota. The cellular microorganisms associated with corals are known to confer benefits to their host by various mechanisms, including photosynthesis, nitrogen fixation, enhancing calcification and infection prevention. Conversely, under conditions of environmental stress, certain microorganisms cause coral bleaching and diseases. Stress responses and tolerance limits of corals are the result of complex interactions with its various symbionts, but the extent to which each member contributes to a particular trait is poorly understood. The viruses associated with corals have received little attention so far, and their diversity and functions in the ecology and evolution of corals are virtually unknown. In my research group, we have started to explore the diversity of coral-associated viruses in a range of coral species on the Great Barrier Reef (GBR), in healthy and diseased/bleached coral tissues, and in laboratory cultures of Symbiodinium isolated from coral. We are examining phages infecting cyanobacteria that associate with coral disease with a long-term view to develop phage therapy for disease treatment. We employ a range of methods including transmission electron microscopy, flow cytometry, PCR amplicon deep sequencing, host genome sequencing and viral metagenomics. Our results show that the viral assemblages of corals are highly diverse; viral families are conserved among scleractinian corals from distinct geographic regions and evolutionary lineages. GBR Symbiodinium cultures have an active infection with a filamentous virus and a ssRNA virus known from free-living dinoflagellates is present in GBR corals. I will present some of the results of our work and discuss new insights gleaned into the roles that viruses play in corals.