Calvin's Case,  Eng.R. 64, (1572–1616) 7 Co.Rep. 1a, 77 E.R. 377—also known as the Case of the Postnati—was a 1608 English legal decision establishing that a child born in Scotland, after the Union of the Crowns under James VI and I in 1603, was considered under the common law to be an English subject and entitled to the benefits of English law. The principles put forth in Calvin's Case were eventually adopted by courts in the United States, and the case played an important role in shaping the American rule of birthright citizenship via jus soli ("law of the soil", or citizenship by virtue of birth within the territory of a sovereign state). However the case has also been cited as providing legal justification for the restriction of legal rights to Native Americans following their conquest by the English.
Under the feudal system, the allegiance owed to a king by his subjects—connected as it was to the holding of interests in land—ruled out the possibility of any given individual holding land in two different kingdoms. Robert Calvin, born in Scotland around 1606, inherited estates in England, but his rights thereto were challenged on the grounds that, as a Scot, he could not legally own English land. The Court of King's Bench ruled in Calvin's favour, finding that he was not an alien and did have the right to hold land in England.
Calvin's Case is in fact a misnomer, since the child "Robert Calvin" was actually named James Colville; he was the son of Robert Colville, Master of Culross, and grandson of the courtier James Colville, 1st Lord Colville of Culross. The test case went to a panel of 14 judges drawn from different courts. Two of those dissented: Sir Thomas Foster (1548–1612) and Sir Thomas Walmesley.
Postnati and antenati
The decision in Calvin's Case hinged on Calvin's status as one of the postnati—subjects born into the allegiance of the Scottish king James after he had become the king of England in 1603—and on the fact that the monarch into whose allegiance he was born (the same James, in his capacity as King of Scots) was also the English king at the time of Calvin's birth—meaning that Robert Calvin, in the judgement of the court, was just as much a subject of the king of England as if he had been born in England instead of Scotland. The judges of the court cited existing statutes—including particularly a 1351 statute, De Natis Ultra Mare, which granted the benefits of subject status to foreign-born children of the king's subjects—as supporting the concept that allegiance was tied to the person of the king, rather than to the kingdom itself or to its laws.
Calvin's Case did not extend English subject status to the antenati (Scots born prior to 1603). They remained aliens in relation to England, on the theory that King James had not yet become the king of England at the time of their birth. Attempts had been made in the English Parliament, prior to Calvin's Case, to naturalise all of James's Scottish subjects—both those born after his English accession in 1603 (the postnati), and also those born before 1603 (the antenati)—but these legislative efforts had been unsuccessful. Concerns had been expressed that extending the privileges of English subjects to all Scots would cause England to be flooded by "an influx of 'hungry Scots'". Objections were also raised that granting naturalisation to all the Scots would have encouraged the legal philosophy, espoused by James, of absolute monarchy and the divine right of kings. Even after Calvin's Case, the English Parliament could have enacted a naturalisation bill covering the antenati, but it never did so.
Although not directly relevant to the case, Coke used the occasion to discuss the position of "Perpetual enemies", specifying "All Infidels are in Law perpetui inimici (Perpetual enemies)" (166). Having accepted that a King who conquers a Christian Kingdom is constrained by the continuance of such laws as exist until new laws are put in place, however " if a Christian King should conquer a kingdom of an Infidel, and bring them under his subjection, there ipso facto the Laws of the Infidel are abrogated, for that they be not only against Christianity, but against the Law of God and of Nature." (170). Robert A. Williams, Jr. argues that Edward Coke used this occasion to quietly provide a legal sanction for the London Virginia Company to dispense with affording Native Americans any rights as they settled in New England. 
Calvin's Case contributed to the concept of the Rights of Englishmen.  Some scholars believed that the case did not fit America's situation, and thus reasoned that the 18th century colonists could "claim all the rights and protections of English citizenship." In fact, one scholar asserts that the legal apologists for the American Revolution claimed they had "improved on the rights of Englishmen" by creating additional, purely American rights.
Owing to its inclusion in the standard legal treatises of the nineteenth century (compiled by Edward Coke, William Blackstone, and James Kent), Calvin's Case was well known in the early judicial history of the United States. Consideration of the case by the United States Supreme Court and by state courts transformed it into a rule regarding American citizenship and solidified the concept of jus soli as the primary determining factor controlling the acquisition of citizenship by birth.
- Coke, Sir Edward. "Calvin's Case, or the Case of the Postnati.". Liberty Fund. Retrieved May 13, 2012. "Ed.: ... someone who was born after James had taken the new [English] throne, who were called the post-nati, a phrase by which the case is often known."
- Price, Polly J. (1997). "Natural Law and Birthright Citizenship in Calvin's Case (1608)". Yale Journal of Law and the Humanities 9: 74. "[Edward] Coke's report of Calvin's Case was one of the most important English common-law decisions adopted by courts in the early history of the United States. Rules of citizenship derived from Calvin's Case became the basis of the American common-law rule of birthright citizenship...."
- Swain, Carol Miller (2007). Debating Immigration. Cambridge University Press. p. 41. ISBN 978-0-521-69866-5. "Nearly all scholarship on the origins of American citizenship acknowledges the singular importance of Calvin's Case in shaping the legal and philosophical principles upon which American citizenship was founded."
- Williams, Robert A. (1990), The American Indian in Western Legal Thought, Oxford; New York: Oxford University Press, ISBN 0195050223, OCLC 18948630, 0195050223
- Price (1997), pp. 81–82.
- Robert Zaller (14 May 2007). The Discourse of Legitimacy in Early Modern England. Stanford University Press. p. 321. ISBN 978-0-8047-5504-7. Retrieved 18 October 2012.
- Williamson, Arthur H. "Colville, James". Oxford Dictionary of National Biography (online ed.). Oxford University Press. doi:10.1093/ref:odnb/67449. (Subscription or UK public library membership required.)
- Lee, Sidney, ed. (1899). "Walmesley, Thomas". Dictionary of National Biography 59. London: Smith, Elder & Co.
- Price (1997), p. 101–102.
- Price (1997), p. 117.
- Price (1997), p. 96.
- Price (1997), p. 97.
- Price (1997), pp. 98–99.
- Price (1997), p. 119.
- Price, Polly J. (1997). "Natural Law and Birthright Citizenship in Calvin's Case (1608)". Yale Journal of Law & the Humanities 9: 73.
- Hulsebosch, Daniel J., The Ancient Constitution and the Expanding Empire: Sir Edward Coke's British Jurisprudence. Law and History Review 21.3 (2003): para. 28-33. Found at History Cooperative website; accessed May 21, 2012.
- Arthur J. Slavin, Craw v. Ramsey: New Light on an Old Debate, in Stephen Bartow Baxter, ed., England's Rise to Greatness, 1660-1763 (University of California Press ), pp. 31-32. Found at Google Books; accessed May 21, 2012.
- Ellen Holmes Pearson, Revising Custom, Embracing Choice: Early American Legal Scholars and the Republicanization of Common Law, in Eliga H. Gould, Peter S. Onuf, ed., Empire And Nation: The American Revolution In The Atlantic World, (Baltimore: Johns Hopkins University Press), ISBN 0-8018-7912-4, p. 102, n. 33; found at Google books, accessed May 21, 2012.
- Price (1997), p. 138–139.
- Harvey Wheeler, Francis Bacon’s Case of the Post-Nati:(1608); Foundations of Anglo-American Constitutionalism; An Application of Critical Constitutional Theory, Ward, 1998