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The Serendipitous Extragalactic X-ray Source Identification (SEXSI) Programis designed to expand significantly the sample of identified extragalactic hardX-ray sources at intermediate fluxes, 1e-13 erg/cm2/s < S_(2-10 keV) < 1e-15erg/cm2/s. SEXSI, which includes sources derived from more than 2 sq deg ofChandra images, provides the largest hard X-ray-selected sample yet studied,offering an essential complement to the Chandra Deep Fields (total area ~0.2 sqdeg). In this paper we describe R-band optical imaging of the SEXSI fields fromthe Palomar, MDM, and Keck observatories. We have identified counterparts, orderived flux limits for nearly 1000 hard X-ray sources. Using the opticalimages, we derive accurate source positions. We investigate correlationsbetween optical and X-ray flux, and optical flux and X-ray hardness ratio. Wealso study the density of optical sources surrounding X-ray counterparts, aswell as the properties of optically-faint, hard X-ray sources.Comment: 30 pages, 8 figures; accepted to ApJ

The Serendipitous Extragalactic X‐Ray Source Identification (SEXSI) Program. II. Optical Imaging