This chapter describes the fundamentals of neuro-electrophysiology. The electrical properties of neuronal membranes can be simulated by equivalent circuits composed of resistance and capacitance. Ion concentration differences across the membrane, combined with varying membrane permeability to ions, form the basis of resting and action potentials. The chapter introduces quantitative membrane indices (including time constant, space constant, rheobase and chronaxie), membrane cable equations, and Hodgkin-Huxley computational model. It also covers electrical stimulation approaches for brain neurons, including intracellular versus extracellular modes, current versus voltage modes, and unipolar versus bipolar modes. Finally, it addresses stimulation safety rules to prevent tissue damage and electrode corrosion.