Nacre the inner iridescent layer of molluscan seashells is a model biomimetic system for design of next generation nanocomposites. Here, we present results of multiscale modelling and experimental investigation of the mechanics of nacre. The structure of nacre which is an organized polygonal laminated platelet structure at the micrometer length scale, is modelled using 3D finite element models and the features up to 50 nm are incorporated into the 3D models. The molecular structure which pertains to the interfacial mechanics of the organic-inorganic interfaces is modelled using steered molecular dynamics. In addition, we have utilized several characterization techniques to evaluate the mechanics of this system at many length scales. Tensile testing and 3-point bend tests are performed at the macro-scale. At the micro-nm length scale we have conducted nanomechanics experiments using atomic force microscopy and nanoindentation. The molecular nature of the organic inorganic interface is investigated using photoacoustic spectroscopy techniques. Our simulations and experiments indicate important results on the specific roles of nano and microstructural details of nacre. We have shown that the organic phase exhibits a very large modulus (∼20 GPa) while also undergoing very large deformations. The mineral bridges that connect one layer of mineral platelets to the next have marginal role on the deformation mechanics of nacre and as also the nanoscale roughness or asperities. We have also discovered the presence of platelet-platelet interlocks in nacre and shown that these interlocks have a very significant role on mechanics of nacre. The deformation of the mineral at nanoscale indicates visco-elastic behaviour which arises from presence of water within and adsorbed on surfaces of the nacre platelets. Our simulations with application of force on molecular models of aragonite and proteins indicate that the deformation of the protein itself is very significantly influenced by the non-bonded interactions that are present at the organic-inorganic interfaces in nacre. These results are significant both for developing understanding of this important material system and also for describing methods and techniques in understanding multiscale mechanics which is applicable and necessary for the next generation advanced material systems.