FSS-based absorbersAbsorber haveElectromagnetic been found to be promising solutions in various applications such as wirelessWireless mobileMobile communicationCommunication, imaging devicesImaging devices, thermal emittersThermal emitters, EM compatibility, and interference. Different configurations of narrowband absorbers, along with their working mechanisms, are discussed. The high Q plasmonic resonanceResonance limits the absorptionBandwidth bandwidthAbsorption bandwidth, and the loading of multiple resonators results in additional absorption bands. Since the resonantFrequency frequencyResonant frequency is hard to anticipate with near-unity absorption, many resonators are loaded to provide perfect absorption at random frequencies. However, it is very difficult to control the near-unity absorptionAbsorption as well as resonant frequencies for the compact unit cell since a loosely loaded resonatorResonators won’t be affected by the problems of mutualCoupling couplingMutual coupling. However, loosely coupled resonators possess large periodicityPeriodicity, and their absorptivityAbsorptivity response is degraded due to the higher-order grating lobesGrating lobes or trapped dielectricDielectric modes at higher oblique angles. This problem has been resolved and discussed by carefully choosing unit-cell periodicityPeriodicity and arranging resonators in such a fashion that both absorptivity and resonant frequency can be controlled are discussed in detail in this chapter.