{mosimage} [[INTEGRAL]] is detecting hundreds of sources in the hard X-rays. Many of them are still unidentified. Comparison with surveys at other wavelengths, together with optical [[spectroscopy]], can reveal their true nature. Using this approach, a program of optical spectroscopy of counterparts of unidentified INTEGRAL sources, ongoing at several observatories worldwide, has allowed the identification of nearly 50 of them. This campaign has been carried out by Iasf-Bo researchers ({cb_profile=masetti}N. Masetti{/cb_profile} et al.), and its results have been choosed as March 2007 Integral Picture of the Month.