  The intelligent reflecting surface (IRS) technology has recently attracted a
lot of interest in wireless communications research. An IRS consists of passive
reflective elements capable of tuning the phase, amplitude, frequency and
polarization of the impinging waveforms. Given such desirable properties, the
wireless channel characteristics can be controlled and optimized for specific
signal design and processing needs -- thus promising significant potential in
radar applications. In this paper, we establish the theoretical foundations for
introducing IRS into a radar system and study the potential to improve target
parameter estimation. More specifically, we will investigate the deployment of
IRS in cases where the line-of-sight (LOS) link is weak or blocked by
obstructions. We demonstrate that the IRS can provide a virtual or
non-line-of-sight (NLOS) link between the radar and target leading to an
enhanced radar performance. The effectiveness of such an IRS-provided virtual
link in estimating the moving target parameters is illustrated under both
optimized and non-optimized IRS scenarios. Numerical simulations indicate that
the IRS can enhance the target parameter estimation when the LOS link is weaker
than $\sim 10^{-1}$ in relative strength in comparison with the NLOS link.
