This book is focused on nonlinear properties of Gallium nanoparticles. The theoretical model of gallium nanoparticle film at the tip of monomode optical fibre has been developed. The interface problem is solved by phase plane analysis, inverse scattering transform method and equivalent particle theory. Effective dielectric constant of gallium nanoparticles on silica substrate has been calculated using into account the Maxwell-Garnett Effective Medium Theory. Minimum power required for Soliton propagation, Stability, shape and size of soliton have also been calculated. Theoretical results have been obtained by applying the perturbation theory for solitons based on the inverse scattering transform method. These investigations have yielded important new insights into all-optical switching devices, upper and lower threshold devices and memory elements. Soliton switch and directional couplers as an application of reflectivity hysteresis due to structural phase transformation in a thin film of gallium nanoparticles on a silica substrate has also been mentioned in the book.