In vitro display technologies, especially ribosome display, are valuable tools for many applications. In this paper, ribosome display technology and its applications for directed evolution of functional proteins will be reviewed. Ribosome display has great potential for directed evolution of protein stability and affinity, the generation of high-quality libraries by in vitro preselection, the selection of enzymatic activities, and the display of cDNA and random-peptide libraries. Ribosome display is carried out fully in vitro, which overcomes some of the limitations of cell-based display systems. We anticipate that ribosome display will have a great impact on applications in biotechnology, medicine and proteomics.