Phage display is one of the most powerful and widely used laboratory technique for the study of protein-protein, protein-peptide and protein-DNA interactions. 

This technology is mainly based on displaying the interest protein (peptides, antibodies, scaffolds or others) on the surface of employing phage and then be used to interrogate the constructed libraries containing millions or even billions of displayed phages. 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.