Periodontitis is associated with the accumulation of plaque and calculus and generally has a slow to moderate rate of disease progression, but periods of more rapid destruction may be observed. Increase in the rate of disease progression may be caused by the impact of local, systemic, or environmental factors that may influence the normal bacterial interaction. The progress of inflammatory periodontal disease, ultimately results in attachment loss sufficient enough to affect the bifurcation or trifurcation of multi-rooted teeth & this is the most serious sequels of periodontitis. The pathogenesis of periodontitis involves a complex interplay between pathogenic bacteria in dental plaque and the host immune-inflammatory response. The etiology, diagnosis, treatment and prognosis of furcation involvement along with various complications faced in management of furcation involved molars are discussed in this book.