Recent computer simulation methodologies are reviewed that attempt to bridge length scales from atomistic scales to macroscopic scales describable by continuum mechanics. Basic concepts of the quasicontinuum method are introduced. Its use of atomistic descriptions at the element level in a finite element code makes possible a seamless transition from atomistic length scales to scales that are orders of magnitude larger. The atomistic description allows crystal geometry to be introduced directly and the generation and propagation of defects to be a natural consequence of the loading. Computational efficiency, relative to molecular dynamics, is obtained by adaptive meshing so that atomistic-scale refinement is used only in regions where the physical fields have steep gradients. Mesh size dependence is essentially eliminated in order to preserve dependence on physical length scales by using all atom positions within the cutoff radii of atomic potentials, even when some of these atoms are in adjacent elements. To model the interaction of many dislocations, discrete-dislocation models are described in which dislocation segments interact through their long range elastic fields. In these models, dislocation dynamics concepts are applied at the level of connected dislocation segments. Bridging of length scales in dynamic fracture is described using a cohesive surface formulation. ©2000 American Institute of Physics.