Thrombocytopenia may result from many causes. Decreased production and decreased survival of circulating platelets due to immune mechanisms are the subject of this chapter. Hemorrhagic risk is typically milder than commonly believed while risks from various treatments can be significant; thus, an enhanced tolerance of the thrombocytopenia in those failing to achieve a remission is rational. The choice of therapeutic interventions depends on the goals of treatment, and can include remission induction or brief elevations of the platelet count at times of trauma, surgery, or other invasive procedures.