Here, the current state of research in scleractinian coral-Symbiodinium symbiosis, the adaptability of Symbiodinium associations to rapid environmental change,and symbiosis evolution is reviewed. Reef corals form associations with an array of genetically and physiologically distinct endosymbiontic dinoflagellates of the genus Symbiodinium. The relationship between zooxanthellae and scleractinian corals is an example of the evolutionary success of such a symbiotic association. Recent molecular phylogenetic studies on the symbionts of coral have revealed an extraordinary diversity of Symbiodinium lineages. Based upon nuclear ribosomal DNA (rDNA) gene polymorphisms, the genus Symbiodinium is currently recognized to comprise at least eight highly divergent phylogenetic clades or lineages (A to H) that in turn contain multiple molecular subclade types. Additional ecological and evolutionary studies have shown that the complexity of these symbiosis. Elucidating the specificity and flexibility between different Symbiodinium and host corals requires additional research. The health of the holobiont is very sensitive to changes in the environment such as elevated sea temperatures due to global climate change. The relationship between corals and Symbiodinium and the adaptability of holobiont are a key area for future research due to the critical challenges that corals,and the reefs they build,face as a consequence of rapid climate change.