Many neural prosthetic devices employ electrode assemblies that are fabricated with biocompatible insulating materials and envelop nerves containing fascicles, which are bundles of axons, our target for controlled neurotransmitter release. The axons in fascicles, serve specific structures, e.g. muscles, and are grouped close together over much of their course in the body between those structures in the peripheral nervous system and the related nuclei in the central nervous system. The grouping works in our favor for selective activation. I’m showing you here a nerve, made up of four fascicles, each containing many axons which may further divide into sub fascicles. Four electrode contacts are included in the figure. When I say Selective Activation I’m thinking about the ability to activate one population of neurons without activating neighboring and unwanted populations that would produce an undesirable side effect. I will be describing two tools to affect this selective activation manipulating the induced electric field, I call Field Steering and utilizing the non-linear properties of voltage gated sodium ion channels.