First published in 1997. This monograph provides a complete overview of the coincidence site lattice model ad its application to grain boundary engineering. Originally propounded several decades ago, the coincidence site lattice (CSL) model has become a cornerstone of grain boundary structure research, particularly in cubic materials. The CSL model has the advantage of being used based on a simple geometrical concept which is easy to visualise and apply in practice. On the other hand here are limitations to the links between CSL geometry and boundary properties. However, with the advent of the new field of grain boundary engineering the CSL model has been shown to be useful and its is therefore timely to review the CSL model in this context.