1. A multi-chain protein display library, comprising a plurality of multi-chain proteins each comprising at least two polypeptide chains, wherein the multi-chain proteins are displayed on a surface of yeast host cells, and wherein the multi-chain proteins are multi-chain T cell receptors, multi-chain MHC class I molecules, multi-chain MHC class II molecules, multi-chain immunoglobulin molecules, or multi-chain biologically active fragments thereof, wherein the multi-chain immunoglobulin molecules each comprise a heavy chain variable region (V H ) and a light chain variable region (V L ), which are on separate chains.