This document provides an overview of organ transplantation, including: 1. A brief history of transplantation from early experiments to modern developments in immunosuppression. 2. Definitions of different types of transplants including autotransplants, allotransplants, and xenotransplants. 3. A discussion of transplant immunobiology including allorecognition and the mechanisms of cellular and humoral rejection. 4. Descriptions of different types of clinical rejection such as hyperacute, acute, and chronic rejection. 5. An overview of commonly used immunosuppressive drugs including corticosteroids, calcineurin inhibitors, mTOR inhibitors, and antiproliferatives.