USD used to be backed by silver (and it was explicitly stated -- see http://www.ebay.com/itm/1957-1-Dollar-Bill-Payable-in-Silver-Historic-Item-Circulated-/4004

USD used to be backed by silver (and it was explicitly stated -- see http://www.ebay.com/itm/1957-1-Dollar-Bill-Payable-in-Silver-Historic-Item-Circulated-/400428359257 http://www.ebay.com/itm/1957-1-Dollar-Bill-Payable-in-Silver... for an example) Nowadays the power of the US government backs the dollar.