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, which stated that "to secure and perpetuate mutual friendship and intercourse among the people of the different States in this Union, the free inhabitants of each of these States . . . shall be entitled to all privileges and immunities of free citizens in the several States; and the people of each State shall free ingress and regress to and from any other State, and shall enjoy therein all the privileges of trade and commerce, subject to the same duties, impositions, and restrictions as the inhabitants thereof."
The Federalist Papers also provides some insight into the clause. Madison's Federalist No. 42. Madison stated: "Those who come under the denomination of free inhabitants of a State, although not citizens of such State, are entitled, in every other State, to all the privileges of free citizens of the latter; that is, to greater privileges than they may be entitled to in their own State . . . ." In Federalist No. 80, Hamilton expressed his belief in the clause's importance when he wrote that the Privileges and Immunities Clause (the version in the Constitution) is "the basis of the union."
Because of the ambiguity of the clause, much debate surrounds the particular rights which the Privileges and Immunities Clause protects. Some scholars believe that it protects the traditional common law rights conferred by particular states to their citizens. The majority opinion in Corfield v. Coryell, however, gives a different approach, stating that the clause protected only certain "fundamental" rights: "Protection by the government; the enjoyment of life and liberty, with the right to acquire and possess property of every kind, and to pursue and obtain happiness and safety; subject nevertheless to such restraints as the government may justly prescribe for the general good of the whole."
The majority opinion enumerates a few specific rights (such as the right to live in and travel through states, the right to sue in courts, etc), but also notes that this is not a comprehensive list.
Corfield became increasingly prominent in later years, particularly in the context of issues like slavery and universal suffrage.