Naturally occurring materials do not necessarily offer electromagneticElectromagnetic (EM) shielding. Hence, unique materials with various compositionsComposition must be synthesized to achieve shielding effectivenessShielding Effectiveness (SE). Once these materials are designed, they must be characterized in the frequencyFrequency range of interest. This chapter delves into the various methods of microwave characterization. The chapter also explains multiple industry-standard characterization methods with real-world examples. A detailed analysis of material properties using the S-parameter system is established. These concepts would give insight to the material designer in designing materials with high absorption. The ideas of Shielding Effectiveness (SEShielding Effectiveness (SE)) are also explored in this chapter, and numerous use cases and real-world examples are provided.