Bone strength is the capacity of bone to resist fracture under mechanical load, determined not only by mineral density but also by bone size, geometry, microarchitecture, and the quality of the collagen matrix. Two bones of equal density can differ markedly in strength if one has thicker cortical walls or better trabecular connectivity. Strength is built through genetics, calcium and vitamin D nutrition, adequate protein, and regular weight-bearing exercise, and it declines with age, inactivity, and hormonal change. In food science and nutrition, bone strength is the functional endpoint behind calcium fortification, osteoporosis-prevention guidance, and dietary recommendations for athletes and older adults.