Decreased platelet counts can be due to a number of disease processes causing decreased platelet production, increased platelet destruction, or can be medication-induced. Health care providers have to differentiate inherited thrombocytopenias, primary immune thrombocytopenias (ITP), secondary immune thrombocytopenias, myelodysplastic syndromes with thrombocytopenia, bone marrow failure syndromes and non-immune thrombocytopenias. ITP is the most common cause of isolated thrombocytopenia. This book focuses on discussing ITP in adults; new treatment for ITP; thrombocytopenia during pregnancy; the different diagnosis of thrombocytopenia; heparin-induced thrombocytopenia; and thrombocytopenia in dengue.