In 1995, serial analysis of gene expression (SAGE) was developed as a versatile tool for gene expression studies. SAGE technology does not require pre-existing knowledge of the genome that is being examined and therefore SAGE can be applied to many different model systems. In this chapter, the SAGE procedure was described, which cannot only be used as a tool to generate gene expression profiles but also to identify new transcripts. SAGE data can easily be exchanged between laboratories and a large database with SAGE data is now available on the internet.