Fault injection is a widely used method to evaluate fault effects and error mitigation in a design. While not a replacement for standard Radiation- Hardness Assurance methodologies, it can provide valuable information in a quick and inexpensive manner. Moreover, recent developments have improved performance by several orders of magnitude, thus enabling the realization of extremely large fault injection campaigns. Today, fault injection can be used to forecast the expected circuit behaviour in the occurrence of SEUs and SETs, validate error mitigation approaches and detect weak areas that require error mitigation. This talk will review the most relevant fault injection methods, covering software-based techniques, simulation techniques and FPGA-based emulation techniques. Recent advances for SET and MCU emulation will also be presented.