Book excerpt: The book covers a wide range of topics pertaining to resonance in optical cavities. The topics include theory, design, simulation, fabrication, and characterization of micrometer and nanometer scale structures and devices that support cavity resonance via various mechanisms such as Fabry-Perot , whispering gallery, photonic bandgap, and plasmonic modes. The chapters discuss optical cavities that resonate from UV to IR wavelengths and are based on prominent III-V material systems including Al, In, and Ga nitrides, ZnO, and GaAs.