Reference: http://www.creative-biolabs.com/phage-display-service.html

Phage display is one of the most widely used laboratory technique for the study of protein-protein, protein-peptide and protein-DNA interactions. This technology is mainly based on the use of filamentous phage which is a kind of virus lives on Escherichia coli and has been proven as a powerful method to interrogate libraries containing millions or even billions of different peptides or proteins. Theoretically, phage display is an exogenous gene expression method which the gene encoding the interest protein is inserted into bacteriophage coat protein gene then displaying the interest protein on the phage surfaces, resulting in a connection between genotype and phenotype. Through DNA manipulation, numerous gene variants can be created and constructed as phage display library. To detect the interaction between displayed protein and those other molecules, phage display library can be screened to against other proteins, peptides or DNA sequences for selecting specific binders.