All objects above absolute zero temperature emit thermal radiation. Seamless control over this thermal radiation can unlock solutions to fundamental and technological challenges in imaging, energy harvesting, and utilization. Existing thermal emitter designs are limited by various trade-offs involving spectral selectivity, brightness, and directionality of thermal radiation. In this thesis, I demonstrate unconventional ways to achieve spectral and spatial control over thermal radiation by engineering complex permittivity of the emitter surface. First, using the principles of non-Hermitian physics, a hybrid plasmonic-photonic coupled resonator metasurface is designed and experimentally verified to exhibit strong spectral selectivity at elevated temperatures. I demonstrate that the designed selective thermal emitter on a refractory metal platform surpasses the spectral efficiency limit set by existing thermal emitter designs used in thermophotovoltaics--a solid-state scheme to convert heat into electricity. A transparent, asymmetrically emitting thermal metasurface is realized based on similar concepts. The designed metasurface enhanced the image contrast while performing thermal imaging in high-temperature environments. Further, the k-space of metasurface is explored, revealing additional tunable parameters for engineering thermal radiation. Finally, a way to achieve broadband IR emission/absorption is proposed and demonstrated using aligned carbon nanotube films with anisotropic permittivity tensor.