Transcription factor IIIA (TFIIIA) is a single polypeptide with several distinct functions in the cell. In this chapter I will review the role of TFIIIA in transcription initiation of the 5S rRNA gene. I will also describe the model by which TFIIIA associates with the 5S rRNA itself to regulate ribosome biosynthesis and assembly. Finally, I will compare these functions of TFIIIA in various eukaryotic cells, from yeast to vertebrate. In all cases, the part played by the protein’s zinc fingers will be emphasized.