The Privileges and Immunities Clause of Article IV, Section 2 of the Constitution states that "the citizens of each state shall be entitled to all privileges and immunities of citizens in the several states." This clause protects fundamental rights of individual citizens and restrains state efforts to discriminate against out-of-state citizens. However, the Privileges and Immunities Clause extends not to all commercial activity, but only to fundamental rights.
There has been a great deal of scholarly debate over the purpose of this constitutional provision. One source of insight as to the purpose of the privileges and immunities clause is its textual predecessor, Article IV of the the Articles of Confederation. This provision was intended to "secure and perpetuate mutual friendship and intercourse among the people of the different states in this Union." Here, the goal of commercial and political integration becomes apparent.
Additionally, much debate surrounds the particular rights protected by the Privileges and Immunities Clause. Some scholars point to traditional common law rights conferred by particular states to their citizens as the rights protected by the clause. Perhaps the most seminal exposition on this topic comes from Justice Bushrod Washington's opinion in the case Corfield v. Coryell. There Justice Washington enumerated those rights he considered to fall under the protection of the Privileges and Immunities Clause. Notably, he indicated that the clause protected only certain "fundamental" rights. This decision became increasingly prominent in later years, particularly in the context of issues like slavery and universal suffrage.