Hypoxia' or decreases in oxygen availability' results in the activation of a number of different responses at both the whole organism and the cellular level. These responses include drastic changes in gene expression, which allow the organism (or cell) to cope efficiently with the stresses associated with the hypoxic insult. A major breakthrough in the understanding of the cellular response to hypoxia was the discovery of a hypoxia sensitive family of transcription factors known as the hypoxia inducible factors (HIFs). The hypoxia response mounted by the HIFs promotes cell survival and energy conservation. As such, this response has to deal with important cellular process such as cell division. In this review, the integration of oxygen sensing with the cell cycle will be discussed. HIFs, as well as other components of the hypoxia pathway, can influence cell cycle progression. The role of HIF and the cell molecular oxygen sensors in the control of the cell cycle will be reviewed.