Vermont resident Kathryn Piper met every New Hampshire bar requirement except residency. The Court struck down the residency rule under Article IV, § 2's Privileges and Immunities Clause. Justice Powell's opinion held that the practice of law is a 'fundamental right' for Clause purposes, that state protectionism against out-of-state lawyers lacks a 'substantial reason,' and that less-restrictive alternatives (like periodic in-state appearances) exist. Piper is the leading modern authority requiring states to justify occupational barriers against nonresidents and it seeded a line of cases opening bars, real-estate practice, and other professions across state lines.