Unveiling the nature of INTEGRAL sources through optical spectroscopy

Since its launch on October 2002 the INTEGRAL satellite is performing an deep survey of the hard X-ray sky with unprecedented sensitivity and positional accuracy. This allowed pinpointing, through positional cross-correlation with catalogs at longer wavelengths, possible optical/near-infrared candidates for the hard X-ray sources of still unknown nature. In this presentation I will describe this work as well as the observational activities aimed at determining, through optical spectroscopy, the nature of the unknown INTEGRAL sources, along with the main results of this search. Future prospects about this identification program will also be illustrated