After a very fruitful collaboration with Raul Gatto at Florence and with Nicola Cabibbo at Rome, Giuliano Preparata's talent exploded on the east cost of the US, at Princeton, Harvard and Rockefeller University, with his pioneering work on the interpretation of the parton model proposed by Feynman in the framework of quantum field theory. Preparata related the observed scaling in the structure functions, which describe deep inelastic scattering, to the singularities on the light-cone of the product of two currents. He also wrote one important paper with Rodolfo Bonifacio about coherent spontaneous emissions, that was the basis for the further developments on quantum field theory of Free Electron Laser, and another, with De Martini, on a related topic. Preparata's masterpiece has been the construction of a theory of coherent phenomena based on quantum electrodynamics and its application to a vast class of problems in condensed matter physics.