Gene Ontology (GO) is a well defined and structured vocabulary to describe gene products of all kind of organisms on three levels: the function of the gene product, the biological process the gene product is involved in, and its localization. In the last years the knowledge of GO increased drastically together with its use to analyse bioinformatic data. Nowadays there exist a large numbers of tools exploiting the GO knowledge to gain more information from bioinformatic and biological data able to provide a “biological picture” of the data set. This workshop will give you insight into the GO and some GO tools such as browsers, annotation and microarray tools. We include extensive hands-on sessions so that the users can test and better understand those tools.