This chapter contains sections titled: Direct Pathway of Allorecognition Structure of the MHC Molecule and Allorecognition Role of Endogenous Peptides in Allorecognition Indirect Pathway of Allorecognition Indirect Allorecognition and Chronic Rejection Endothelial Cells and Allorecognition Site of Allorecognition Role of Allorecognition in the Effector Phase of Allograft Rejection Allorecognition Pathways and the Induction of Tolerance Conclusions References