Fletcher v. Peck,
10 U.S. 87 (1810)
http://www.oyez.org/oyez/resource/case/124/Facts of the Case: In 1795, the Georgia state legislature passed a land grant awarding territory to four companies. The following year, however, the legislature voided the law and declared all rights and claims under it to be invalid. In 1800, John Peck acquired land that was part of the original legislative grant. He then sold the land to Robert Fletcher three years later, claiming that past sales of the land had been legitimate. Fletcher argued that since the original sale of the land had been declared invalid, Peck had no legal right to sell the land and thus committed a breach of contract.
Question Presented: Could the contract between Fletcher and Peck be invalidated by an act of the Georgia legislature?
Conclusion: In a unanimous opinion, the Court held that since the estate had been legally "passed into the hands of a purchaser for a valuable consideration," the Georgia legislature could not take away the land or invalidate the contract. Noting that the Constitution did not permit bills of attainder or ex post facto laws, the Court held that laws annulling contracts or grants made by previous legislative acts were constitutionally impermissible.