Platelets are one of the components of the blood along with white and red blood cells. Platelets play an important role in clotting and bleeding. The number of platelets in the blood is referred to as the platelet count and is normally between 150,000 to 450,000 per micro litre (one millionth of a litre) of blood. Platelet counts less than 150,000 are termed thrombocytopenia. Platelet counts greater that 450,000 are called thrombocytosis. In the present book we will discuss different points concerning platelets functions, abnormalities and therapeutic modalities for thrombocytopenia.