The periodontitis disease is multifactorial (complex) and its susceptibility is influenced both by genetic and environmental factors. Periodontitis is also associated with many types of syndromes and genetic disorders. Segregation analysis indicated autosomal dominant transmission of the disease. It is believed that various forms of aggressive periodontitis are due to single gene defects that are inherited as autosomal dominant disorders with incomplete penetrance. However, some other studies indicated the X-linked inheritance. Even though segregation studies have shown different modes of inheritance, they all support the involvement of genes in the causation of the disease. Twin studies indicated a significant genetic influence on various parameters of periodontal disease. Linkage studies for periodontitis by various workers have indicated the presence of genes on different chromosomes i.e., on chromosome number 4 (4q 11-13), 11 (11q14) and 1 (1q25). Association studies for periodontitis have indicated a positive association between aggressive periodontitis and HLA–A9 and B15 antigens. Many workers have found the positive association between periodontitis and interleukin-1 gene polymorphism; association between tumour necrosis factor and periodontitis; association between IgG2 production and periodontitis. At the end of the chapter genetic basis of various syndromic form of periodontitis are discussed.