Platelets perform numerous important functions not only in the process of normal functioning of hemostatic system, but also in other physiological processes, such as: vessel wall integrity regulation, wound healing, inflammatory response. Its malfunction can be found in various diseases and conditions (including oncohematological disorders, solid tumors, inflammatory diseases, sepsis, autoimmune disorders), is triggered by injury or medications and can lead to dangerous consequences, such as bleeding and thrombosis. However, platelets functional activity quantity assessment tools are extremely limited, the perception what platelet functional activity is about is also quite unclear. This review considers platelets function, its' abnormalities, possibilities for its' assessment by existing methods as well as promising directions for their development.