This paper explores some of the major categories of monetary theories and theories of money. It defines the essence, the origin, and, to a large extent, the nature of money, classifies monetary theories, substantiates some concepts of classical quantity, cash balance, liquidity preference, pure monetary theories. It introduces the notions of monetary chartalism, monetary commoditizatonalism and monetary constitutionalism into the scientific use. It proves fiat essence of modern money. It applies praxiological approach to money research. Debatableness of money itself is shown.