This book provides a series of methods for flexibly and actively manipulating thermal emission and photoluminance by advanced nanostructures—metamaterials. Nanostructures in subwavelength scales can be designed to precisely modulate light-matter interactions and thereby tailoring both thermal radiations and photon emissions. This book explores approaches for designing different kinds of nanostructures, including multilayers, gratings, nanoridges, and waveguides, to improve the flexibility and functionality of micro/nanodevices. With the help of these subwavelength nanostructures, thermal radiation and photoluminescence have been fully manipulated in near and far fields regarding to the intensity, spectrum, polarization, and direction. The proposed methods together with designed metamaterials open new avenues for designing novel micro-/nanodevices or systems for promising applications like thermal energy harvesting, detecting, sensing, and on-chip quantum-optical networks.