The High-Pressure High-Temperature (HPHT) sintering is an established process for reclaiming Waste Tire Rubber (WTR) into Magnetorheological Elastomers (MREs). Even though the WTR is generally recycled to other products, the usage of WTR as the main matrix of MRE is a new and novel concept. Therefore, this book focuses on studying the physicochemical and viscoelastic properties of the WTR based MRE produced through HPHT process. The WTR, carbonyl iron particles, and additives were mixed and compacted by applying simultaneous temperature and pressure at 200 deg-C and 25 MPa, respectively. Swelling test, morphological examination, infrared spectroscopy, magnetization, and thermal analysis were among the physicochemical properties studied. Meanwhile, the magneto-induced viscoelastic properties were assessed through shear mode test in both steady and dynamic conditions.