Nanoscience is a broad interdisciplinary area of research, development and industrial activity which has been growing rapidly world wide for the last few decades. The particles in this particular size regime display characteristic physical, chemical and optoelectronic properties, which are strikingly different from those of the corresponding bulk materials. Recently, physicists and chemists are interested in the electronic structure of metal and semiconductor nanoparticles because of the quantum size effect, which has been shown to appear in that size range. As the size of a material is reduced down to nanoscale dimension, the electronic structure of the material changes from continuous energy bands of the bulk state to discrete energy levels of the atoms. This book tells us the wet chemical route for the synthesis of well ordered aggregates of metal nanoparticles of variable sizes using different ligand. The effect of nanoparticle size on the nature of aggregation as well as the variation in the optical response due to variable degree of interparticle coupling effects amongst the gold particles have been investigated.