In this Article, I offer a new framework for understanding federalism. “Vectoral federalism” engages directional metaphors—horizontal and vertical—to group various federalism doctrines together into two principal groups.Horizontal federalism concerns the battle between the federal and the state governments for the power to regulate individuals. Vertical federalism concerns the federal government’s power to regulate states and the states’ concomitant power to resist this regulation. Viewing federalism doctrines as having vertical or horizontal vectors (or both) identifies their common justifications and characteristics, which can assist in understanding and in applying the principles of federalism. The directional synthesis also illuminates and helps to rectify the Court’s errors. Vectoral federalism has the potential to become an important tool for understanding American federalism and for developing a more unified and coherent federalism doctrine