The study of the properties of charged dislocations in semiconductor crystal is now a large independent field of semiconductor physics. Latest investigations indicate that changes in the electronic subsystem of II-VI semiconductors significantly effect the motion of dislocation.The photoplastic effect in crystalline materials has been extensively investigated over the last two decades. The phenomena of photoplastic effect (PPE), photoplastic after-effect (PPAE) and photoplastic memory effect (PPME) have attracted a lot of attention for the last four decades. A systematic measurement of PPE and PPAE has been made on alkali halides, I-VII compounds, II-VI semiconductors, III-V semiconductors, group IV semiconductors, and on several organic materials, particularly on polymers.Although significant experimental works have been made on the photoplastic effect, least theoretical studies have been made on this.It is expected that this book will be useful to understand the influence of electronic states on the crystal plasticity and the basic process involved in the degradation in the electronic devices.