Spectroscopy of catalyst systems under actual operating conditions, or operando spectroscopy, has become instrumental in helping to determine the structures and mechanisms of catalytic systems. Operando spectroscopy is differentiated from in situ spectroscopy in that operando spectroscopy occurs under the actual catalyst operating conditions. In addition, a measure of the catalyst activity is also critical during operando spectroscopy. Operando spectroscopy has revealed that some catalytic systems operate under much different conditions than previously believed based on ex situ analysis. We present some of our recent work using operando XAFS of catalytic systems varying from hydrogen release of hydrogen storage materials to benzene hydrogenation. We present a basic introduction into XAFS and its use as an operando technique and show how this technique can be used to differentiate between catalyst containing highly dispersed nanoparticles and organometallic clusters.