This book provides an overview of nanocomposite materials that can be used as embedded dielectric layer in high-density electronic packaging, for decoupling, filtering, energy storage or electrostatic discharge suppressing, etc. Some fundamental models used to analyze or predict the dielectric behavior of ceramic/polymer, conductor/polymer, and semiconductor/polymer composites are reviewed. This book also introduces design and synthesis of some novel hybrid filler particles, as well as graft modification on the polymer matrix to improve dielectric performance.