Although a significant amount of evidence has demonstrated that there are intimate connections between transcriptional controls and cell cycle regulation, the precise mechanisms underlying these connections remain largely obscure. A number of recent advances have helped to define how critical cell cycle regulators, such as the retinoblastoma family of tumor suppressor proteins and the cyclin-dependent kinases, might function on a biochemical level and how such mechanisms of action have been conserved not only in the regulation of transcription by all three RNA polymerases but also across species lines. In addition, the use of in vivo techniques has begun to explain how the activity of the E2F transcription factor family is tied to the cell cycle dependent expression of target genes.