This lecture delves into the mathematical framework of the Hodgkin-Huxley equation, exploring how to model neurons in principle and the challenges of choosing parameters for specific neurons. It discusses the underlying biophysics of electrical behavior, the distinction between passive and active membrane mechanisms, and the representation of the membrane as an electrical circuit. The lecture also covers the implications of the cable equation, the spatial discretization of neural models, and the use of computers to solve complex neuron modeling problems.