During the last 10 years we have developed new tools that make possible to study the crystallographic and electronic structure of surfaces in vacuum and under gas environments up to atmospheres and temperatures of several 100 degrees C. They include Scanning Tunneling and Atomic Force Microscopies (STM and AFM), and photoelectron spectroscopies (XPS, NEXAFS, RIXS). We apply these techniques to studies of sruface reactions. I will illustrate the power of these techniques with examples that include: O, CO and NO adsorption and reaction on Rh and Pd, the reactions of acetylene to form benzene, methanol and oxyged to form formaldehyde and finally the formation and decomposition of water on Ru, Pd and Cu.