The use of modeling to simulate the effects of electrical stimulation on the nervous system can improve the development and use of neuroprosthesis devices, avoid long adjustment tests during the implantation surgery, and select a priori relevant parameters that could improve the benefits of stimulation and reduce side effects. In this chapter, we will focus on ways to model the nervous system in response to electrical stimulation, starting with electrical properties of the neuron membrane and ending with complex biophysics models representing the whole nerve trunk. Modeling of the peripheral nerve is a huge topic, and the first computational model could be considered to be almost 70 years old from the work of Hodgkin and Huxley. From this key starting point, both the membrane electrophysiological behavior and the biophysics of the conductive tissue get increased interest and accuracy. Finally, with the rise of more and more powerful computers and numerical solvers, it is now possible to gain insight into the intimate functioning of the axon and the nerve electrophysiological behavior. It could be used in two ways, from traveling action potentials to recording electrodes or from stimulating electrodes through current injection to action potential delivery. The chapter focuses on the second topic knowing that almost all the modeling frame is valid to achieve the inverse problem. We thus detail the method to model the biophysics and then the membrane dynamics up to the axon level through detailed equations and examples. The extension to the spinal cord or brain neural network is not introduced even though the basics remain similar.