This chapter discusses the simulation of susceptibility and immunity testing, with a focus on modeling various laboratory sources and calibrating them for different test scenarios. The chapter begins with the simulation of bulk current injection (BCI), demonstrating how both open-loop and closed-loop calibration can be achieved within a simulation. Following calibration, we apply the BCI methodology in an application example involving an automotive Ethernet system subjected to a BCI test. Next, we introduce signal generators used for burst, surge, and pulse testing. In the second part of the chapter, we focus on radiated immunity testing. We begin by introducing the absorber-lined shielded enclosure (ALSE) test setup using a biconical log-periodic antenna and compare the simulation results to a simplified setup in which excitation is applied using a plane wave. We then investigate the effect of layout imbalance on the voltages induced during radiated immunity testing. The final section of the chapter presents a simplified model of a TEM cell, which is used to study coupling into bond wires of a simple IC package.