Studies done on the skin's blood circulation have also resulted in the development of new, more complex flaps. This complexity has made a standardized classification of flaps no longer possible. As a result of this, we have tried to analyze the inner system of flaps. This analysis has made a connection between the construction and the vascular structure of the flaps evident. Based on the fundamental construction and basic vascular structure, we are able to divide the flaps into three elementary types. All the complex flaps are composed of these three elementary types. This composition takes place in the form of a parallel connection or in the form of a sequential connection of the elementary types or both. To ensure the adequate blood supply of a flap, it is necessary to maintain the continuity of the elementary vascular patterns.