In this paper, we examine various models of monetary systems. By using the ideal currency concept, we show that the two-tiered model of monetary system currently used in almost all countries has serious flaws, the root cause of which is the use of private currencies issued by banks. It is shown that from the perspective of the economy of the digital society, the optimal model of monetary system is one with a single-tiered architecture and a single currency system in which circulates sovereign currency issued by the Central Bank. An important distinctive feature of this model is that the monetary system is completely decoupled from the banking system, thereby preventing propagation of risks inherent to the banking business to the underlying economy.