Abstract The process of cutting of a grain boundary by a gliding or climbing dislocation is considered. Some planar dislocation arrays with long-range stress fields are also treated. Defects formed on the grain boundaries by these mechanisms include edge and screw disconnections, grain boundary dislocations, spacing defects and line forces. The cutting defects can also acquire kinks and jogs. The results have implications for emission of lattice dislocations from grain boundaries, trapping of dislocations at grain boundaries and grain boundary topography.