Chapter 6 focuses on MIMO antennas for UWB applications. As a MIMO system deals with multiple antennas installed in a common platform, along with the conventional antenna figure of merits, it must qualify against some additional parameters such as envelope correlation coefficient (ECC), diversity gain (DG), mean effective gain (MEG), total active reflection coefficient (TARC), etc. After a brief overview of MIMO antenna parameters, the design of UWB-based MIMO antennas is considered. This is based on various contemporary contributions and can be broadly classified into planar UWB-MIMO antennas and dielectric resonator-based UWB-MIMO antennas. In addition, the chapter includes two sections dedicated to frequency-notched MIMO antenna design and isolation-enhancement techniques in MIMO antennas.