Phage display can be used to generate human antibodies to virtually any antigen. This requires a number of crucial steps that are common to all molecular diversity technologies: the creation of diversity, coupling of phenotype (antibody protein) to genotype (antibody gene), selection, amplification, and analysis (reviewed in ref. 1–3). Antibodies with affinities comparable to those obtained using traditional hybridoma technology can be selected from either large naïve antibody libraries or from immune phage antibody libraries. The affinity of initial isolates can be further increased, to levels unobtainable in the immune system, by using the selected antibodies as the basis for construction and selection of libraries in which the antibody gene is diversified (see Chapters 19 and 20). This approach is one of the few methods for generating fully human antibodies, especially to evolutionarily conserved or self proteins (4). Although in theory there are many different choices to be made when constructing a phage antibody library, most published work has followed a tried and tested formula. In particular, filamentous phage-based phagemid vectors have been used almost exclusively, and the phage minor coat protein pIII has been the display coat protein most frequently used (2,5). Libraries have been made using both the single-chain Fv (scFv) (6–10) and Fab format (11,12).