cDNA display is a robust and versatile in vitro protein selection tool developed on the basis of mRNA display. In this tool, a protein is covalently linked with its coding cDNA via a specially-designed puromycin-linker to improve the stability of the molecule. As a result of the stabilization, cDNA display succeeded in extending the variety of libraries (e.g., modified peptide library) and target molecules (e.g., cell surface molecules). Thus, this technology will enable to design functional proteins and peptides which could not be evolved by the previous in vitro protein selection tools.