Phage display allows the presentation of large peptide and protein libraries on the surface of filamentous phage, which leads to the selection of peptides and proteins, including antibodies, with high affinity and specificity to almost any target. The technology involves the introduction of exogenous peptide sequences into a location in the genome of the phage capsid proteins. The encoded peptides are expressed or "displayed" on the phage surface as a fusion product with one of the phage coat proteins. This way, instead of having to genetically engineer different proteins or peptides one at a time and then express, purify, and analyze each variant, phage display libraries containing up to 10¹⁰ variants can be constructed simultaneously. Phage particles withstand very harsh conditions, such as low pH and low temperatures, without losing bacterial infectivity. Thus, protocols using low pH and high concentration urea have been used to dissociate bound phage from a target. In addition, bound phage does not need to be eluted from a microtiter well or animal tissue before bacterial infection. Instead, infection can proceed after addition of bacteria directly into the well or to the homogenized organ or tissue.

The strength of phage technology is its ability to identify interactive regions of proteins and other molecules without preexisting notions about the nature of the interaction. The past decade has seen considerable progress in the applications of phage display technology. Different screening methods have allowed isolation and characterization of peptides binding to several molecules in vitro, in the context of living cells, in animals and in humans (Arap 2002b). Here we review the applications, as well as recent innovations and future directions of phage display technology.