This chapter first accurately reviews the basics of smart microgrid protection since the definitions vary from a reference to another. Then it focuses on the fault responses of Inverter-Based Resources (IBR’s) as those are emerging technologies that will be playing the great role of interfacing primary energy resources and the grid. In particular, for materialization of net-zero Carbon emission in electricity generation, the use of IBR’s is indispensable. However, the non-universal and software-defined IBR fault responses make conventional relays such as overcurrent, directional, and distance relays inapplicable in heavily IBR-based grids. Therefore, the discrepancy between conventional and IBR fault responses is elaborated and possible solutions to the looming protection issues are discussed. The shortcomings and merits of each solution are also discussed.