Peter Gill has made both fundamental and applied contributions to the progress of quantum chemistry. His development of efficient two-electron integral algorithms, perturbation analysis, linear-scaling methodology, DFT functionals, theory of excited states, Coulomb-splitting techniques, and the Q-Chem software package, have significantly changed the research tools of the field. His models for three-electron bonding and dication dissociation have been widely adopted by experimentalists. His insights into electron correlation and the nature of the uniform electron gas are changing the underlying paradigms of density functional theory (DFT). For these and other advances, he has received four international medals.