Filamentous bacteriophage offers the possibility of linking genotype with phenotype in one genetic package. By creating a library of different proteins as fusion to one of the coat proteins of filamentous bacteriophage it becomes possible to isolate proteins based on their binding characteristics. Phage displayed libraries of varying formats, ranging from small peptides to antibody fragments, have been selected successfully for ligands toward a large panel of targets. These peptides and antibody fragments are applicable in analysis of the behaviour of certain proteins with respect to changes in biological processes such as aging, thus providing valuable tools for a general understanding of the aging process. Alternatively, display of antibody fragments or peptides on filamentous bacteriophage can be instrumental in the discovery of novel antigens as exemplified by selections on cell surfaces or on complex protein mixtures such as sera from aging individuals. Although phage display has been applied successfully in a large number of studies relating to cancer, viral infections and other biological processes, its application in the field of aging research is yet to be realised.