One of the universal features of solid tumours is the presence of hypoxic cells as tumours outgrow their blood supply. These cells make tumours resistant to radiotherapy and chemotherapy, as well as selecting for a more malignant phenotype. The transcription factor hypoxia inducible factor-1 (HIF1) is an important regulator of the growing tumour's response to hypoxia, as it activates genes that allow cancer cells to survive and grow in the hostile hypoxic tumour environment. It is now just a decade since the discovery of HIF1 and the underlying molecular pathway, and the first cancer therapeutics targeting this pathway are now entering the clinic. This Therapy Focus highlights the development of these drugs.