Over the last half century, developments in optics have fundamentally transformed the way we live. For example, optical communications has helped bring people across the globe closer, while consumer electronics, in the form of CDs and DVDs, have allowed us to store, access, and share information on a scale that was believed unattainable several decades ago. While innumerable technologies have been developed across the electromagnetic spectrum, one specific frequency band has largely been underdeveloped. The far-infrared or terahertz (THz) frequency range has often been referred to as the gap in the electromagnetic spectrum. This book describes our research in exploring the physics and applications of resonance phenomena at THz frequencies using surface plasmon based artificial resonant structures. Because of their unique properties and potential device applications, these artificial media, referred to as plasmonic metamaterials, have attracted significant scientific interest over the last few years. This book would serve as an excellent reference for graduate students and scientists working in these as well as other areas of electrical engineering, physics and material sciences.