This book provides a thorough investigation of near-field heat transfer between parallel plates separated by a vacuum gap of nanometer distances which has potential applications in energy conversion devices, nanofabrication, and near-field imaging. Near-field heat transfer between doped Si plates at varying doping levels is calculated using the improved dielectric functions developed through this dissertation. The near-field energy transfer between two semi-infinite media is maximum when the real part of dielectric function is around -1 due to the excitation of surface waves. The optimized Drude model always results in greater near-field heat transfer compared to the Lorentz model and the maximum achievable near-field heat transfer is nearly 1 order greater than that between real materials. Unlike far-field radiation, the penetration depth in near-field heat transfer is dependent on the vacuum gap. This unusual feature results in a 10 nm thick SiC film behaving as completely opaque at 10 nm vacuum gap. The energy streamlines inside the emitter, receiver, and the vacuum gap are calculated which helps to decide the physical dimensions of the media exchanging thermal radiation