In this book, the authors discuss the theory of operation, behaviour and safety regulations of capacitors. The topics include (CCTO) ceramics as potential candidates for capacitor applications; devices, materials and mechanisms of capacitive sensors for gas and humidity detections; an overview of the leakage current mechanisms of ultra-thin gate dielectrics used in new-age capacitors and transistors; integration of capacitors into integrated circuits; and the impact of capacitor energization over the power quality of the MV distribution grid.