This book deals with a comprehensive analysis of the results obtained from structural, optical, electrical and magnetic studies of differently treated ZnO. Discussions over the defect dynamics, generation, characterization and interrelation of defects with different physical properties in ZnO system have been explored in the various chapters of the book. Introduction of the book is given in Chapter One. The Chapter Two consists of descriptions of different experimental techniques employed for the present study. Effect of Mn doping on the structural, optical, electrical and magnetic properties of ZnO has been reported in Chapter Three. In Chapter Four, we report the mechanical milling induced modifications of structural, morphological and optical properties of polycrystalline ZnO powder sample. Modification of structural and optical properties and also change in defect configuration due to 1.2 MeV Ar ion irradiation on polycrystalline ZnO powder sample have been reported in Chapter Five. This book might cater to the needs of the researchers working in the field of defect and physical property characterization of II-VI and other semiconductors.