A method of identifying a cognate binding moiety of one or more antigens, said method comprising the steps of: a) providing 1) a population of cells, each of said cells comprising: i) a cell surface antigen and ii) a nucleic acid comprising a first recombination motif, and 2) a plurality of attachment-defective virions, each of said virions comprising: i) one of a plurality of transgenic viral surface binding moieties and ii) a nucleic acid comprising a second recombination motif capable of integrating with said first motif; b) contacting said population of cells with said virions, wherein, if one or more of said virions comprise a cognate binding moiety of one or more of said cell surface antigens, binding of said cell surface antigen and said cognate binding moiety results in selective infection by the bound virion of the cell comprising said cell surface antigen of said cognate binding moiety; c) incubating said population of cells under conditions sufficient to allow recombination between said first and second recombination motifs in infected cells, thereby generating a recombinant product; and d) identifying a cognate binding moiety of one or more of said antigens by identifying the nucleic acid sequence of said recombinant product or an identifying fragment thereof, in a cell, and identifying from said nucleic acid sequence an antigen and a cognate binding moiety. a) providing 1) a population of cells, each of said cells comprising: i) a cell surface antigen and ii) a nucleic acid comprising a first recombination motif, and 2) a plurality of attachment-defective virions, each of said virions comprising: i) one of a plurality of transgenic viral surface binding moieties and ii) a nucleic acid comprising a second recombination motif capable of integrating with said first motif; 1) a population of cells, each of said cells comprising: i) a cell surface antigen and ii) a nucleic acid comprising a first recombination motif, and i) a cell surface antigen and ii) a nucleic acid comprising a first recombination motif, and 2) a plurality of attachment-defective virions, each of said virions comprising: i) one of a plurality of transgenic viral surface binding moieties and ii) a nucleic acid comprising a second recombination motif capable of integrating with said first motif; i) one of a plurality of transgenic viral surface binding moieties and ii) a nucleic acid comprising a second recombination motif capable of integrating with said first motif; b) contacting said population of cells with said virions, wherein, if one or more of said virions comprise a cognate binding moiety of one or more of said cell surface antigens, binding of said cell surface antigen and said cognate binding moiety results in selective infection by the bound virion of the cell comprising said cell surface antigen of said cognate binding moiety; c) incubating said population of cells under conditions sufficient to allow recombination between said first and second recombination motifs in infected cells, thereby generating a recombinant product; and d) identifying a cognate binding moiety of one or more of said antigens by identifying the nucleic acid sequence of said recombinant product or an identifying fragment thereof, in a cell, and identifying from said nucleic acid sequence an antigen and a cognate binding moiety.