Swelling clays have properties which are detrimental to civil infrastructure and also have properties which are sought by petroleum, environmental, pharmaceutical and nanocomposite materials industry. Macroscale properties of clay largely depend on molecular level interactions and its microstructure. Developing understanding and tools for bridging length scales for predicting and tailoring properties of swelling clays has been the primary focus of this paper. Steered molecular dynamics simulations are used to evaluate the mechanical response of dry and hydrated sodium montmorillonite. The mechanisms of clay water interactions are found, the nature of water in the interlayer, contribution of various constituents of the system to the properties are evaluated quantitatively. Fundamental parameters necessary for steered molecular dynamics simulations are calculated. A new discrete element modelling technique incorporating particle subdivision is developed for accurate modelling of evolution of microstructure in swelling clays. Complimentary experimental techniques at various length scales using fourier transform infrared spectroscopy, atomic force microscopy, nanoindentation, X-ray diffraction, scanning electron microscopy and swelling and swelling pressure response obtained using a specifically designed controlled swelling cell provide verification as well as guide modelling. These unique and essential experimental and modelling interconnects allow for accurate bridging of length scales.