Systemic risk, its elements and quantification methods as one of the starting points to the analysis of the specific role of big financial entities (especially banks). Theoretical approaches to big financial entities; problem of size and the concept of systemic importance. Ways to a better understanding of the four “C”s - contagion, correlation, concentration, and conditions. Network theories and the identification of a systemic importance. The big financial entities´ potential impact on the macroeconomic financial stability of a country. The main criteria of SIFIs´ classification and selection. The national versus international dimensions of SIFIs´ regulation. Selected policy problems of SIFIs´ regulation. A comparison of the proposed different regulatory measures.