In this chapter, the multiple input multiple output (MIMO) antenna designs with some unique metamaterial structures (MTMS) are discussed. The different features of metamaterials implemented in antenna designs are presented. The diversity parameters of MIMO antenna are significantly improved with MTMS. Furthermore, this chapter also covers the different techniques used to model the different MTMS and a comparative study is also presented. The significance of MTMS-based MIMO antenna in technological applications such as high-speed communication, Internet of Things (IoT), robotics, smart sensors, and wearable electronics are also discussed.