Most solid tumors develop regions of hypoxia as they grow and outstrip their blood supply. In order to survive in the stressful hypoxic environment, tumor cells have developed a coordinated set of responses orchestrating their adaptation to hypoxia. The outcomes of the cellular responses to hypoxia are aggressive disease, resistance to therapy, and decreased patient survival. A critical mediator of the hypoxic response is the transcription factor hypoxia-inducible factor 1 (HIF-1) that upregulates expression of proteins that promote angiogenesis, anaerobic metabolism, and many other survival pathways. Regulation of HIF-1alpha, a component of the HIF-1 heterodimer, occurs at multiple levels including translation, degradation, and transcriptional activation, and serves as a testimony to the central role of HIF-1. Studies demonstrating the importance of HIF-1alpha expression for tumor survival have made HIF-1alpha an attractive target for cancer therapy. The growing l.ist of pharmacological inhibitors of HIF-1 and their varied targets mirrors the complex molecular mechanisms controlling HIF-1. In this chapter, we summarize recent findings regarding the regulation of HIF-1alpha and the progress made in identifying new therapeutic agents that inhibit HIF-1alpha.