The structure of materials is set by phenomena that occur on length scales from the atomic to the continuum.  Moreover,  the time scale of a simulation that is accurate over a certain length scale is often overly restrictive. Thus, predicting the evolution of a material is both a multi spatial-scale and a multi temporal-scale problem.  An introduction to the challenge posed by multiscale modeling of materials will be given.  A particularly promising approach that addresses the timescale limitation associated with multiscale materials modeling is the Phase Field Crystal (PFC) method.  This approach removes the short timescale limitation of molecular dynamics, but retains its atomic scale spatial resolution. The method allows atomic scale motion and defect formation to be determined on diffusive timescales. Using the PFC approach, the structure and dynamics of an important defect in materials, grain boundaries, has been examined. We find that the atomic-scale structure of the boundary gives rise to qualitatively new grain growth kinetics as well as to both grain rotation and translation. The grain translation is a result of the climb, glide, and interactions of the dislocations that comprise the grain boundary, as well as dislocation interactions at trijunctions.  The effect of temperature and vacancy concentration on grain boundary structure, migration, and grain-boundary pinning will also be discussed.