Dislocations are lines of irregularity in the structure of a solid analogous to the bumps in a badly laid carpet. Like these bumps they can be easily moved, and they provide the most important mechanism by which the solid can be deformed. They also have a strong influence on crystal growth and on the electronic properties of semiconductors.·Influence of dislocations on piezoelectric behavior·New mechanisms for hardening in twinned crystals·Bringing theories of martensite transformation into agreement·Atomic scale motion of dislocations in electron microscopy·Dislocation patterns deduced from X-ray diffraction·Role of dislocations in friction·Dislocation motion in quasicrystals