One way to improve the selectivity of therapeutic molecules in clinical oncology would be to target them on the tumour site, thereby sparing normal tissues. The development of targeted therapeutic methodologies relies in most cases on the availability of binding molecules specific for tumour-associated markers. The display of repertoires of polypeptides on the surface of filamentous phage, together with the efficient selection-amplification of the desired binding specificities using affinity capture, represents an efficient route towards the isolation of specific peptides and proteins that could act as vehicles for tumour targeting applications. Most investigations in this area of research have so far been performed with phage derived recombinant antibodies, which have been shown to selectively target tumour-associated markers both in preclinical animal models and in the clinic. However, future developments with other classes of polypeptides (small constrained peptides, small globular proteins) promise to be important for the selective delivery of therapeutic agents to the tumour site.