"United States Currency" has been upgraded and will become a part of the Whitman Collector Series as the ninth edition of the popular reference goes on sale.

International currency arrangements have come under scrutiny in the aftermath of the global financial crisis The dollar has been the preeminent global reserve currency for most of the past century.

Read on to learn more about the dollar's unofficial status as the world's currency, why it is so popular, and how U.S. dollars that move into and out of the U.S. are tracked. Dollarization is the ...