This is a 7 minute long interview with sustainable development economist Richard Werner. He explains how the largest portion of the money in circulation today has been created out of nothing from loan-agreements between banks and their customers, all the while supported by the government and central banks. Very interesting and surprising!
This constantly growing creation of money, based merely on promises to pay back money, is perhaps not the most sustainable economy to build a society on say many (especially economists from the austrian school).
For further introductory information go to the article on the fractional banking system on wikipedia (http://en.wikipedia.org/wiki/Fractional_reserve_banking)