A wider range of materials has emerged since 1965, most notably in the field of electronics and micro-engineering. The principles of dislocation theory still apply but some of the detail requires further treatment.This fourth edition provides an essential basis for an understanding of many of the physical and mechanical properties of crystalline solids. This new edition has been extensively revised and updated to reflect developments in the understanding of the subject, whilst retaining the clarity and comprehensibility of the previous editions.