This course explains basic experimental and theoretical principles of measuring single plasmonic nanoparticle linear and nonlinear cross sections. Plasmonic nanoparticles have become important nanoagents for biolabelling, photothermal cancer therapy, data storage and sensing. Their extraordinary heat transduction and nonlinear luminescence capability is highly dependent in accurate measurement of individual absorption/scattering cross sections. This course will be overviewing the current existing methods of measuring extinction, scattering and absorption cross sections of these nanoparticles, both linear and nonlinear, equipping students and researchers to understand energy efficiencies of interested processes within a single nanoparticles. The knowledge is then translated to applications in two-photon imaging and dark-field imaging.