Three Americans have won the 2007 Nobel Prize for economics: Leo Hurwicz from the University of Minnesota; Eric Maskin of Princeton University; and Roger Myerson of the University of Chicago. The U.S. academics won for their work in Mechanism Design Theory, which studies the efficiency of the marketplace by looking at factors such as the quality of information made available to market participants.
The Nobel committee has published a document called "Information for the Public" that attempts to explain their accomplishments in laymen's terms. A more academic background paper on Mechanism Design Theory is also available online.
If you're really interested, the Nobel committee has also published citations for the key academic papers that brought the winners to prominence.
The link for the above information.