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We present optical spectroscopy of a sample of 77 luminous AGN and quasarsselected on the basis of their mid-infrared colors. Our objects are selectedfrom the Spitzer Extragalactic First Look Survey and SWIRE XMM-LSS fields, witha typical 24mu flux density of 5mJy. The median redshift is 0.6, with a rangeof ~0.05-4. Only 33% (25/77) of these objects are normal type-1 quasars, withno obscuration. 44% (34/77) are type-2 objects, with high-ionization, narrowemission lines, 14% (11/77) are dust-reddened type-1 quasars, showing broadlines but a dust-reddened or unusually weak quasar continuum. 9% (7/77) show nosign of an AGN in the optical spectrum, having either starburst spectra orspectra which could be of either starburst or LINER types. These latter objectsare analogous to the X-ray detected population of AGN with weak or non-existentoptical AGN emission (the ``XBONGs''). 21 of our objects from the SWIRE fieldfall within moderately-deep XMM exposures. All the unobscured quasars, andabout half the obscured quasars are detected in these exposures. This sample,when taken together with other samples of Spitzer selected AGN and quasars, andresults from X-ray studies, confirms that obscured AGN dominate the AGN andquasar number counts of all rapidly-accreting supermassive black hole systems,at least for z~<4. This implies a high radiative efficiency for the black holeaccretion process.Comment: 30 pages, 10 figures (some color), accepted by A

the astronomical journal

Optical Spectroscopy and X-Ray Detections of a Sample of Quasars and Active Galactic Nuclei Selected in the Mid-Infrared from Two<i>Spitzer Space Telescope</i>Wide-Area Surveys

Optical Spectroscopy and X-Ray Detections of a Sample of Quasars and Active Galactic Nuclei Selected in the Mid-Infrared from TwoSpitzer Space TelescopeWide-Area Surveys