The transplantation of organs such as the heart, kidney, and lungs is an important means of replacing seriously damaged or diseased body parts. However, a transplanted organ may fail if the recipient's immune system mounts a response to it. Transplant patients are usually prescribed a life-long course of immunosuppressive medication, but these drugs can have adverse effects, including increased risk of infection and cancer. Written and edited by experts in the field, this collection from Cold Spring Harbor Perspectives in Medicine provides a current and comprehensive review of the molecular...