  Recent progress in approaches to determine the elastic constants of solids
starting from the microscopic particle interactions is reviewed. On the
theoretical side, density functional theory approaches are discussed and
compared to more classical ones using the actual pair potentials. On the
experimental side, video microscopy has been introduced to measure the elastic
constants in colloidal solids. For glasses and disordered systems, the
theoretical basis is given for this novel technique, and some challenges and
recent advances are reviewed.
