This article discusses immunosuppressive medications used in organ and hematopoietic stem cell transplantation. Induction, maintenance, and rescue therapy are administered throughout different periods during and after transplantation to modulate the immune system response in the recipient to prevent or treat rejection or graft-versus-host disease. Indications, dosing strategies, required monitoring, complications, adverse events, and concomitant drug interactions associated with immunosuppressive medications are presented. Classes of medications discussed include polyclonal and monoclonal antibodies, calcineurin inhibitors, antiproliferative agents, mammalian target of rapamycin inhibitors, and corticosteroids. Medications having significant interactions with immunosuppression are also examined.