The books gives a survey of FMIs theory and selected practical issues.The book is divided into four parts. Part One presents the introduction to the theory of financial markets infrastructures (FMIs). The origin of the word "infrastructure" is explained and different FMIs definitions discussed. Two concepts of FIMs are compared: a theoretically based "broad" concept, and a "narrow" concept based on IOSCO pragmatic approach enabling the selected elements of FMIs to be regulated. My "broad" concept of a theory of FMIs embraces three interconnected elements, i.e. a qualitative characteristic of a FMI, FMIs typology and classification, and a general model of modern FMIs development. The FMI is presented as a system, whose elements are closely connected. In the Part Two of the monograph, the role of international organisations which are involved in the FMIs regulation (either directly or indirectly) is analysed. In the monograph´s Part Three, a comparative analysis of selected international organisations features and activities´ scopes is presented.In the Part Fourth of the monograph, the 5 FMIs subsystems (according to the IOSCO concept of the FMIs system) are – one by one – described, analysed and discussed