End user computing (EUC) is like dark matter in physics. EUC is enormous in quantity and importance yet has been largely invisible to corporate IT departments, information systems (IS) researchers, and corporate management. EUC applications, especially spreadsheet applications, are also “dark” in the sense that they pose a number of overlooked risks for organizations, including errors, privacy violations, trade secret extrusions, and compliance violations. On the positive side, EUC applications are also like the dark energy of physics. They are supporting critical gains in decision making, computing by scientists and engineers, operational systems, and other important processes in every corner of the firm. It is time to stop ignoring end user computing in general and spreadsheets in particular. The purpose of this paper is to document to the extent possible today then importance of end user computing relative to the concerns of corporate IT departments and IS researchers.