A dielectric material is an electrical insulator that can be polarised by an applied electric field. Dielectrics are insulators, plain and simple. The two words refer to the same class of materials, but are of different origin and are used preferentially in different contexts. The plastic coating on an electrical cord is an insulator. The glass or ceramic plates used to support power lines and keep them from shorting out to the ground are insulators. Pretty much anytime a nonmetallic solid is used in an electrical device it's called an insulator. Perhaps the only time the word dielectric is used is in reference to the non-conducting layer of a capacitor. When a dielectric is placed in an electric field, electric charges do not flow through the material as they do in a conductor, but only slightly shift from their average equilibrium positions causing dielectric polarisation. Because of dielectric polarisation, positive charges are displaced toward the field and negative charges shift in the opposite direction. This creates an internal electric field that reduces the overall field within the dielectric itself. If a dielectric is composed of weakly bonded molecules, those molecules not only become polarised, but also reorient so that their symmetry axes align to the field. The study of dielectric properties concerns storage and dissipation of electric and magnetic energy in materials. Dielectrics are important for explaining various phenomena in electronics, optics, and solid-state physics. This book endeavours the theory and practice of dielectric materials for various types of industrial applications.