This paper describes the time-domain (TD) ultra-wideband (UWB) microwave imaging radar system developed at the University of Illinois at Urbana-Champaign recently. The TD-UWB imaging radar system successfully combines the UWB impulse radar system and inverse scattering imaging algorithms for nondestructive evaluation (NDE) and remote sensing purposes in the near-field region. Both the system hardware and inverse scattering algorithms of the system will be discussed in this paper. The TD-UWB imaging radar system can detect dielectric or metallic targets located in air or shallow subsurface with a high resolution image reconstruction capability. Reconstructed images of different types of targets are shown to be in good agreement with the target geometry. The experimental results demonstrate the potential of the system as an useful tool for NDE and remote sensing applications.