"What are the effects of free trade and globalization? What are the driving forces behind worldwide urbanization? Paul Krugman has formulated a new theory to answer these questions," the academy said in its citation.
"He has thereby integrated the previously disparate research fields of international trade and economic geography," it said.
Krugman was the lone of winner of the 10 million kronor (US$1.4 million) award, the latest in a string of American researchers to be honored.
The award, known as the Nobel Memorial Prize in Economic Sciences, is the last of the six Nobel prizes announced this year and is not one of the original Nobels. It was created in 1968 by the Swedish central bank in Nobel's memory.