After the sequencing of the human genome is completed, the research focus shifts toward the analysis of gene products. The human genome encodes more than 30,000 genes. Owing to alternative mRNA splicing and posttranslational modifications, for example, glycosylation, phoshorylation, and so on, the number of different proteins of human proteome is supposed to easily exceed 90,000. Antibodies are key detection reagents for the "postgenomic" analysis of these proteins. Any systematic investigation of the human proteome requires high throughput methods for antibody generation. In vitro selection systems utilizing recombinant antibody repertoires offer this capability and capacity. The most commonly used contemporary in vitro selection system is antibody phage display, which has already yielded thousands of useful antibodies for therapy, research, and diagnostics. Herein, methods are described for the selection of recombinant antibody fragments from naive antibody gene libraries.