Prince William asked Queen Elizabeth II for her consent when he wanted to marry Kate Middleton.  While this seems quaint, it is required by the Royal Marriages Act of 1772.  According to the official website of the British Monarchy, King George III insisted on this law because he was disappointed in the marriages of his brothers.  Interesting side note, this was the same king that "lost" the colonies in the American Revolution.

The Act of Settlement (passed in 1700 and enacted in 1701) states that Roman Catholics, or anyone married to a Roman Catholic, cannot hold the Crown.  This law was meant to secure Protestant succession and maintain the Church of England.  These and other interesting materials are part of a mini display in the Wolff Library.  Look for the high table near the computers on the lower level of Wolff.