Hypoxia is a common feature of many cancers. It contributes to local and systemic tumour progression as well as potentially compromising radiotherapy and chemotherapy. Hypoxia-inducible factor 1 (HIF-1) is an essential component in changing the transcriptional response of tumours under hypoxia. It targets the transcription of over 60 genes involved in many aspects of cancer biology including cell survival, glucose metabolism, cell invasion and angiogenesis. Over-expression of HIF-1 has been associated with increased patient mortality in several cancer types including breast, stomach, cervical, endometrial and ovarian cancers. The pharmacological manipulation of HIF-1 has marked effects on tumour growth, and it could prove to be an important target for drug therapy, both in cancer and in other hypoxia-dependent disease states.