It has been known for quite some time that cancer cells undergo far-reaching modifications in their metabolism, yet a full understanding of these changes and how they come about remains elusive. Even under conditions of plentiful oxygen, cancer cells choose to switch glucose metabolism from respiration to lactic acid formation. The mystery behind the molecular mechanisms of this phenomenon, known as the Warburg effect, is now being unravelled. The reduced respiration rate and increased glucose uptake associated with lactic acid production, and acidosis of the micro-environment, are primarily due to activation of the alpha/beta hypoxia-inducible transcription factor. This distinctive metabolic nature of cancer cells is already being exploited as a diagnostic tool but is yet to be harnessed as a therapeutic intervention.