In this book the most important issues concerning normal operation and ground fault phenomena are described in concise form. Numerous methods of insulation resistance and capacitance measurement in live circuits are presented. Important other procedures of these parameters determination based on measurement and calculation are explained and reviews of selected insulation resistance measurement devices as well as earth fault locating systems are included. This book is addressed to electrical engineers, technicians and students and may also serve as an academic handbook. The extended second edition includes several innovative methods of insulation parameters determination as well as more detailed explanations of procedures and issues. Furthermore new important problems e.g. indirect methods of insulation resistance determination and insulation resistance monitoring in networks with frequency converters are addressed as well as examples of practical applications.