Crystal structures of T-cell receptors (TCRs) and B-cell receptors (BCRs) in complex with their cognate antigens illustrate the critical role of CDRs in antigen recognition. (A) Structure of the 1G4 TCR in complex with the NY-ESO-1_157-165 peptide and HLA-A*02:01.¹  The first, second, and third CDRs (CDR1, CDR2, and CDR3) of the 1G4 α chain are colored magenta, orange, and red, respectively, to enable easier visualization, and the corresponding regions of the 1G4 β chain are colored blue, cyan, and green. (B) Structure of the broadly neutralizing 10E8 anti-HIV gp41 antibody antigen-binding fragment in complex with a gp41-derived peptide.²  The CDR1, CDR2, and CDR3 of the 10E8 heavy chain and the corresponding regions of the 10E8 light chain are colored magenta, orange, red, blue, cyan, and green, respectively. The structures in (A) and (B) were rendered with PyMOL.³