In an extreme case, virtual currencies could have a substitution effect on central bank money if they become widely accepted. The increase in the use of virtual money might lead to a decrease in the use of “real” money, thereby also reducing the cash needed to conduct the transactions generated by nominal income. In this regard, a widespread substitution of central bank money by privately issued virtual currency could significantly reduce the size of central banks’ balance sheets, and thus also their ability to influence the short-term interest rates. Central banks would need to look at their existing tools to deal with this risk (for instance, trying to impose minimum reserve requirements on virtual currency schemes).