"In the United States, the Secret Service works to prevent the counterfeiting of U.S. currency."
Felkenes, George T. "Counterfeiting." World Book Online Reference Center. 2005. World Book, Inc. 25 Oct. 2005 .

"Money is anything that is generally accepted by people in exchange for the things they sell or the work they do. Gold and silver were once the most common forms of money. But today, money consists mainly of paper bills, coins made of various metals, and checking account deposits."
Doty, R. G., and Stanley Fischer. "Money." World Book Online Reference Center. 2005. World Book, Inc. 25 Oct. 2005 .

Brief Counterfeiting Information
"History of Counterfeiting." United States Secret Service. 1 Jan. 2002. United States Secret Service. 25 Oct. 2005 .