Almost all electronic materials generally exhibit a majority carrier type, either electrons or holes, that dominates the transport uniformly along all directions of the crystal. These p-type and n-type regions are then integrated together to separate and control the flow of charge to create virtually all modern electronic and energy harvesting devices. Here, we will describe our recent work in the synthesis, properties, and applications of materials that exhibit, simultaneously, either dominant n-type or p-type conduction depending on the direction of travel. We will establish the origin of this exotic behavior and the band structure design principles for creating new materials that with this axis-dependent conduction polarity. This understanding has led us to rapidly expand the number of materials that experimentally exhibit this behavior. Finally, we will show that the unique charge separation inherent in these materials can overcome limitations in existing electronic and energy-harvesting devices, leading to exciting new technologies.