This chapter examines the propriety of federal laws under the power most often invoked to justify restrictions on liberty: the power to regulate commerce among the several states. Courts are not empowered to disregard powers that are expressly enumerated in the Constitution, even those that violate the rights of the people. They are authorized only to interpret the meaning of these powers, and where this meaning is underdeterminate, to construe them in a manner that is consistent with original meaning and that would render their exercise as legitimate as possible. The chapter analyzes the federal power to regulate commerce by explaining what the Commerce Clause means. It also considers judicial interpretations of commerce during the period 1824–1935 and shows that the term “among the states” independently limits federal power with respect to commerce. Finally, it reviews John Marshall's arguments in Gibbons v. Ogden.