An important role for melatonin in bone formation and restructuring has emerged, and studies demonstrate the multiple mechanisms for these beneficial actions. Statistical analysis shows that even with existing osteoporotic therapies, bone-related disease, and mortality are on the rise, creating a huge financial burden for societies worldwide. These findings suggest that novel alternatives need to be developed to either prevent or reverse bone loss to combat osteoporosis-related fractures. The focus of this review describes melatonin's role in bone physiology and discusses how disruption of melatonin rhythms by light exposure at night, shift work, and disease can adversely impact on bone. The signal transduction mechanisms underlying osteoblast and osteoclast differentiation and coupling with one another are discussed with a focus on how melatonin, through the regulation of RANKL and osteoprotegerin synthesis and release from osteoblasts, can induce osteoblastogenesis while inhibiting osteoclastogenesis. Also, melatonin's free-radical scavenging and antioxidant properties of this indoleamine are discussed as yet an additional mechanism by which melatonin can maintain one's bone health, especially oral health. The clinical use for melatonin in bone-grafting procedures, in reversing bone loss due to osteopenia and osteoporosis, and in managing periodontal disease is discussed. ; the female-to-male ratio for fracture is 1.6 [1]. In the European Union, approximately 22 million women and 5.5 million men (between 50 and 84 yr) are projected to have osteoporosis; this number will rise by 23% by 2025 [3]. In the United States, nearly 57 million adults over age 50 are affected by bone disease, 48 million adults have osteopenia, and 9 million adults have osteoporosis, which places these individuals at risk for developing bone fracture. If left unchanged, by 2030, the prevalence of osteoporosis will increase to 11.9 million and 64.3 million with osteopenia [4].In the United States, the annual fracture rate is 1.5 million per year (300,000 hip and 700,000 vertebral fractures), which is expected to increase by 3 million by 2025 [5,6]. In the United Kingdom, although it was expected that the 12-month survival rate after hip fracture would be 90-91%, the actual numbers were less than expected with 63.3% of men and 74.9% of women surviving [7]. In the United States, hip fracture is responsible for approximately 31,000 excess deaths within 6 months, which can start as early as age 50; this is significant, considering that one in every three women and one in five men in the United States will experience an osteoporosis-related fracture in their lifetime [6]. In addition to increasing morbidity and mortality rates, osteoporosis-related fractures are also creating huge economical burdens to societies worldwide. For example, osteoporosis treatment and related fracture cost in the United States (per year) is $19 billion, which is expected to increase to $25.3 billion by 2025 [6]. In 2010, osteoporosis-related costs amounted ...