The present invention relates to a library of particles, the library displaying a plurality of different T cell receptors (TCRs), wherein the plurality of TCRs consists essentially of TCRs comprising an alpha chain comprising an alpha chain variable domain and a beta chain comprising a beta chain variable domain and the library comprises more than one TRAV gene product and/or more than one TRBV gene product, wherein the beta chain variable domain does not comprise one or more of a TRBV5-1, 5-3, 5-4, 5-5, 5-6, 5-7 or 5-8 gene product and wherein the plurality of TCRs do not consist essentially of TCRs comprising a TRAV12-2 gene product from a natural repertoire and a TRBV6 gene product from a natural repertoire and TCRs comprising a TRAV21 gene product from a natural repertoire and a TRBV6 gene product from a natural repertoire.