Final Report Summary - IMCOLMAT (Impurities in Colloidal Materials - tuning the properties of crystals, powders and glasses) Pure materials are an extreme rarity in nature as almost every material contains some sort of impurity, whether present as an unavoidable nuisance or intentionally added to modify a product or process. The ability to use the effect of impurities for the design of new materials remains a formidable challenge and crucially depends on our fundamental knowledge of the underlying structural and dynamical processes in materials. In this project we have used colloidal model systems, in which particles of a few micrometers are dispersed in a molecular solvent, to study the behaviour of crystalline, polycrystalline and glassy materials and how this behaviour is affected by the presence of impurities. In particular, we have studied the motion of the interface between different crystallites, a crucial process in crystal growth, how this motion is affected by the presence of impurities, which are distributed in the polycrystalline network. We also developed techniques to directly measure the force by which impurities are pinned to these interface. In addition, we have found that small crystallites embedded in a large crystal can only exist under certain conditions, which are a direct consequence of the geometry of lattice. We furthermore established how crystals of two-dimensional hard spheres melt and studied the diffusive dynamics of both single and multicomponent hard spheres fluids. Finally, we measured the interactions of impurities embedded in a fluid of other particles, and characterized the structure and dynamics of the fluid particles around these impurities. Overall, our work has contributed to a better understanding of the behaviour of interfaces in crystals, the melting of crystals and the structure and dynamics of crystalline and fluid-like systems and the effect of impurities thereon. We believe this will be relevant for the successful design and development of new materials.