Glucose and glutamine metabolism in cancer cells are markedly elevated relative to non-transformed normal cells. This metabolic reprogramming enables the production of adenosine triphosphate and the anabolic precursors needed for survival, growth and motility. The recent observations that mutant oncogenic proteins and the loss of tumor suppressors activate key metabolic enzymes suggest that selective inhibition of these enzymes may yield effective cancer therapeutics with acceptable toxicities. In support of this concept, pre-clinical studies of small molecule antagonists of several metabolic enzymes in tumor-bearing mice have demonstrated reasonable therapeutic indices. We will review the rationale for targeting metabolic enzymes as a strategy to treat cancer and will detail the results of several recent clinical trials of metabolic inhibitors in advanced cancer patients.