Microwave/millimeter-wave techniques such as interferometry, reflectometry, scattering, and radiometry have been powerful tools for diagnosing magnetically confined high-temperature plasmas. Important plasma parameters were measured to clarify the physics issues such as stability, wave phenomena, and fluctuation-induced transport. Recent advances in microwave and millimeter-wave technology together with computer technology have enabled the development of new generation of diagnostics for visualization of 2D and 3D structures of plasmas. Microwave/Millimeter-wave imaging is expected to be one of the most promising diagnostic methods for this purpose. We report here on the recent progress in microwave diagnostics and the results obtained in magnetically confined plasmas.