This chapter mainly focuses on two broad categories ofPolarization converters metamaterialMetamaterials-based applications in the THz frequencyFrequency range, absorbersAbsorber and polarizationPolarization converters. Researchers have gained a lot of interest in THz technology due to its possible use in various applications such as sensing, communicationCommunication, and imaging. MetasurfacesMetasurface were meticulously engineered to allow absorbers to efficiently absorb EM waves in the THz regime, resulting in enhanced absorptionAbsorption qualities. This study provides an in-depth evaluation of the design criteria, such as unit-cell architecture, material selection, and arrangement, intending to achieve high absorption over a wide frequencyFrequency range. The design, simulation, and characterization of absorbers are mainly addressed in this chapter, which delves into their vital roles for THz devices. Furthermore, this chapter also investigates polarizers which manipulate the EM waveWave polarization in the THz range. The anisotropic metasurfaces enable polarization conversion and have many advantages compared to naturally available crystals like quartz and tourmaline, such as wide bandwidthBandwidth and minimal losses. In addition, different polarizer applications are detailed as reported in the literature.