95% of the Indian population suffers from periodontal disease. The periodontal disease is caused by invasion of microbes on the tooth surface which leads to the activation of the host immune response. This periodontal war is thus a battle of two kingdoms – The Host and the Microbes and is a never–ending process. Over the years pathogens have developed resistance against the immune responses of the host giving them an edge to flourish and cause more widespread and virulent disease. This review article focuses on understanding the changes in host immune system following microbial insult which leads to periodontal destruction. The etiology of periodontitis and role of keystone pathogen has also been highlighted.