Engineering thermal emission using micro/nanostructures has received growing attention in recent years. A variety of novel coherent, directional, polarized and narrowband thermal light sources as well as wavelength selective emitters have been proposed and investigated. These emitters show a great potential in applications like thermophotovoltaics, solar energy concentration, radiative cooling, thermal detection, sensing, thermal camouflage, thermal rectification, etc. In this article, we give a review on the use of micro/nanostructures to control far-field thermal emission. Thermal emitters based on various micro/nanostructures including gratings, photonic crystals, metamaterials and metasurfaces are reviewed and some important applications are summarized. We expect this article can provide a general overview of this field.