The key to modify or enhance radiative properties is to employ one-, two-, or three-dimensional (1, 2, or 3D) periodic micro/nanostructures, but very few comprehensive studies are available. The present work numerically and experimentally investigates the radiative properties of micro/nanostructures and explores their potential applications such as absorptance of patterned wafer in rapid thermal processing, wavelength-selective radiator design, and nanolithography. The theoretical foundation was built upon the rigorous coupled-wave analysis (RCWA) for numerical calculation of the far-field radiative properties and the electromagnetic field distribution in the near-field regime. Measurements of diffraction efficiencies were conducted on fabricated 1D and 2D periodic silicon microstructures with a high resolution laser scatterometer/diffractometer. A parametric study of radiation absorption from nanoscale patterned wafers was performed to evaluate the applicability of simplified models such as the effective medium approximation for semiconductor manufacturing application. Next, a new concept of complex gratings was proposed for actively tailoring the radiative properties for the design of a wavelength-selective thermophotovoltaic radiator. Furthermore, nanoscale metallic slit arrays were shown to exhibit polarization-dependant transmission characteristics and localized electromagnetic energy density for potential application of nanothermal manufacturing. Three submicrometer slit arrays were fabricated and their spectral transmittance was measured with a Fourier-transform infrared spectrometer. The results largely agree with RCWA predictions. This dissertation clearly demonstrates that precise control and tuning of the radiative properties using micro/nanofabrication are not only feasible but also may have numerous technological impacts.