The Multiple-Input and Multiple-Output (MIMO) radars are categorized into two distinct structures, containing the Colocated Antennas (CA) and the Widely separated Antennas (WSA). Generally, Multi-antenna radars provide a higher degree of freedom than conventional single-input and single-output radars owing to the use of multiple transmitters and receivers with different waveforms. In WSA configuration, the spatial and waveform diversity enable the radar systems superiority in detection and estimation of target parameters. This Thesis focuses on target localization problem by the use of MIMO radar systems configured with widely distributed over an area. According to researches, target localization methods can be Keywords : Multiple-Input and Multiple-Output (MIMO) Radars, Localization, Weighted Least Squares (WLS), Approximate Maximum Likelihood (AML)