Dielectric and electrical conductivity properties are very important since the associated physical properties. In this book, an attempt made to elucidate the dielectric and conductivity properties of BNT and BNT-based materials. The conductivity of an ionic conductor is determined by both the concentration of the mobile ions and the rate at which they are able to hop from site to site in the material. Impedance spectroscopy is a useful technique to analyze the electrical properties of low conductivity materials and electro-ceramics. This is particularly relevant for poly-crystalline ferroelectric materials in which the temperature dependent variation of the capacitance associated with the ferroelectric component explains high value of the dielectric constant at Curie temperature.