The identification of a gene, whether by a genetic screen or through a genome sequencing project, is only the first step in the long journey to determining the role of that gene in the cell. Many different experimental methods can be used to get from detecting the presence of an open reading frame (ORF) in a piece of DNA to an understanding of what the protein encoded by that gene actually does. In this chapter, we will focus on the approaches that involve gene cloning methods, but you should bear in mind throughout that these are only a part of the tool box available to biological scientists.