This tutorial addresses modeling and simulation of protection circuit elements and networks under ESD conditions. The high current characteristics and transient responses of devices typically used in ESD protection circuits will be presented. The objective is to ascertain what behaviors have to be captured in models intended for circuit-level simulation of ESD. Specific examples of model implementations will be provided. Parameter extraction and model scalability will be addressed. Thermal modeling will be discussed, as will the issue of modeling the off-state behavior of ESD protection devices.