Recently, the production and applications of metal nanoparticles have rapidly been increased in the field of nanotechnology. The properties of metal nanoparticles strongly depend upon their size and shape. Moreover, as metal nanoparticles easily aggregate each other, it is difficult to prepare them at high concentration. This book provides the novel method of preparing finely size-controlled and highly concentrated silver nanoparticles in organic solvents by introducing solid-liquid reverse micellar extraction. As the preparation of metal nanoparticles by solid-liquid reverse micellar extraction does not require a special apparatus and extreme conditions of temperature and pressure, it is comparatively easy to expand the scale in the production of nanoparticles. Therefore, this book should help not only in the fundamental research using metal nanoparticles but also in the large scale production of them.