On April 23, 2010, Arizona enacted S.B. 1070, which is designed to discourage and deter the entry or presence of aliens who lack lawful status under federal immigration law. This report discusses this piece of legislation and some of the notable preemption issues raised by its provisions. Where relevant, it examines the district court's ruling that the federal government is likely to succeed on the merits of its arguments that certain sections of S.B. 1070 are preempted by federal law. It also discusses other preemption issues potentially raised by S.B. 1070 or similar legislation, including some issues that were not expressly addressed by the district court in its preliminary ruling.