Recent years have seen the rapid spread of prepaid IC-type electronic payment methods known as electronic money, including Suica, ICOCA, PASMO, SUGOCA, Kitaca, Edy, nanaco, WAON, and others. The inclusion of the word "money" in the name has led to a perception of privately issued "money" being used as an alternative to cash, especially in small denominations. It is sometimes argued that privatelyissued "money" will steal the seigniorage that the government and the Bank of Japan earn by issuing cash, or that private companies will be able to earn seigniorage. As things stand, it is clear that e-money is a type of payment method that requires a charge of cash and is not a substitute for cash itself.It is also true, however, that in recent years there have been reports that the balance of small-denomination money in circulation has declined due to the impact of electronic money's replacing it. On the other hand, there is a view that the decline in small-denomination money has been affected by structural changes in Japan, such as the introduction of fee-based bank ATMs, in addition to electronic money.The purpose of this chapter is to empirically examine the impact of e-money on the amount of money in circulation by type of money, taking into account as much as possible the structural changes in the financial system, including policy changes such as the increase in the consumption tax rate and the introduction of bank ATM charges.We would also like to discuss how widespread e-money actually is, what the characteristics of e-money are nationally, and what the prospects for its future are, as well as what the policy issues surrounding e-money are.