In this chapter, we first give a short introduction to auroral conjugate studies since the 1960s. We do not intend to give a review of the earlier findings because such papers already exist, but we will describe in some detail new results from the last couple of years based on global imaging in the UV wavelengths by the IMAGE and Polar satellites. We review the results from a paper showing how the interplanetary magnetic field (IMF) clock angle, θ c , or IMF B y can be used to organize the

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... orm locations in the conjugate hemispheres and how they give slightly different information. Then, we report a study where complete asymmetric aurorae were observed. Based on the results from these two papers, we discuss the interhemispheric currents that can be associated with these observations. We present three candidates for producing such currents that are related to IMF orientation, B y and B x , and tilt angle. The three candidates are (1) the penetration of IMF θ c or B y into the closed magnetosphere, (2) the differences in solar wind dynamo efficiency due to IMF B x and tilt angle, and (3) the conductivity differences due to tilt angle. We claim that all these candidates are consistent with our recent observations.