Immune thrombocytopenia (ITP) is an autoimmune disorder characterized by increased platelet destruction and impaired platelet production from bone marrow megakaryocytes. The details of different platelet destruction mechanisms resulting from differences in autoantibodies and autoantibody-independent direct platelet destruction remain unclear although antiplatelet autoantibodies directed against platelet glycoproteins, such as GPIIb/IIIa and GPIb, play a central role in ITP pathogenesis. ITP is diagnosed by excluding other causes of thrombocytopenia due to the lack of standard tests or biomarkers for its confirmation. Plasma thrombopoietin level measurement and reticulated platelet ratio are useful in distinguishing the cause of thrombocytopenia and will be included in the new "Diagnostic reference guide of adult immune thrombocytopenia." Currently, the treatment of refractory chronic ITP is mainly based on thrombopoietin receptor agonists, but ITP drugs with novel mechanisms of action are actively developed. New therapeutic agents are expected to be selected based on an accurate diagnosis and tailored to the pathophysiology of each case in ITP treatment.