In the last decade, the study of nanoparticle (NP) systems has become interesting research area due to their novel properties and functionalities, which are different from those of the bulk materials, and also their potential applications in many different areas. The direct measurement of the electrical properties of metal NPs presents a key challenge and necessitates the use of innovative experimental techniques. There have been numerous reports of four point resistance measurements of NPs films. However, using novel microwave techniques such as the coaxial probe and dielectric resonator for electrical characterisation of metallic NPs, more accurate and effective results can be obtained compared with other traditional techniques. This book describes the microwave properties of metallic NPs, obtained using these techniques. It is expected to be of benefit to researchers involved in synthesis and materials characterisation of metal NP systems. It should also be useful to researchers in other disciplines, such as materials scientists and electrochemists, who wish to understand the capabilities and limitation of synthesis and characterisation techniques that they use.