Periodontal diseases range from the relatively benign gingivitis to chronic and aggressive forms of the disease. Bone resorption is a basic physiologic process that is central to the understanding of many key pathologies, with its most common oral manifestation seen as the alveolar bone destruction in periodontitis. This review described the mechanisms of bone resorption as related to periodontal disease, at the molecular and cellular levels. Key words: Bone loss, Periodontitis, Osteoclasts