This chapter discusses the properties of M13 and its life cycle, the production of phage-displayed antibodies, and the advantages of using such antibodies. The M13-infected E. coli host cell acts like a factory to constantly produce M13 phage components. The production of M13 phage-displayed recombinant antibodies involves genetically linking deoxyribonucleic acid (DNA) from antibody-producing B-lymphocytes or hybridomas to the phage gene 3 DNA. The chapter describes the general procedure used to produce phage-displayed recombinant antibodies. Messenger RNA (mRNA) from antibody-producing B-lymphocytes or hybridomas provides the template for production of recombinant antibodies. Phage-displayed recombinant antibodies have several advantages over polyclonal antibodies or hybridoma-derived monoclonal antibodies. Recombinant antibody technology represents a new approach which can be used to quickly develop inexpensive immunological reagents. The antibody mRNA serves as a template for reverse transcriptase to generate a complimentary strand of DNA (cDNA) n a first-strand cDNA reaction.