The human oral microbiome plays an important role in host physiology. The causes and factors that influence the microbiota are closely linked to the cause of a disease. Some oral taxa, especially Porphyromonas gingivalis and Fusobacterium nucleatum, induce carcinogenesis by several different mechanisms, like inhibiting apoptosis, inducing cell proliferation, cellular invasion, migration and chronic inflammation. These changes are seen parallel with the malignant lesions developed in the oral cavity. Starting with a brief introduction on eubiosis and dysbiosis of oral microbiome this chapter has highlighted the role of structural and metabolic attributes of bacteria in oral carcinogenesis via influencing the eight established hallmarks of cancer.