Bone is an essential biological nanocomposite found in the human body that plays a vital role in providing structural integrity and mobility to the human body. Bone displays structural hierarchy spanning from the molecular scale to the macroscale, beginning with well-organized arrays of collagen molecules and nanoscale hydroxyapatite which in turn form the fibrils followed by concentric lamella and the osteon and finally the macroscopic bone. The role of molecular interactions between the nanosized hydroxyapatite and collagen on the mechanics of collagen is evaluated using molecular dynamics simulations. In addition, detailed steered molecular dynamics studies on the mechanics of full length collagen of 300nm size, are conducted and the impact of inter-chain molecular interactions on the structure of collagen and mechanics on the collagen are mechanistically evaluated. The mechanical response obtained from molecular scale studies are incorporated into a 3D finite element model of fibril using a hierarchical multiscale modeling approach. Simulations using the finite element models of collagen fibril are conducted to study the elastic and inelastic response of the fibril. These simulations provide an insight into key mechanisms that influence the mechanics of fibril and indicate that the molecular scale interactions at collagen-mineral interfaces have a significant impact on the mechanics of the fibril. Further, we report the role of crosslink densities in collagen fibrils on the mechanics of the fibril. These studies are vital towards understanding ageing and diseases in bone.