Since the discovery of the first variable stars in the 16th century, their study has been one of the principal areas of astronomical research. During the 20th century and the beginning of the 21st, many optical photometric surveys have been carried out with the aim of understanding the physical mechanisms producing the observed variations of brightness. With the discovery of the first X-ray sources in the sky in the 60’s and the development of X-ray astronomy, several X-ray observatories have been launched into space in order to study the properties of these X-ray sources at higher energies. Multiwavelength analyses are required for a better knowledge of these systems. For this reason, an optical monitoring camera was included on the X- and gamma-ray space observatory INTEGRAL of the European Space Agency (ESA). In this thesis, the main results of the analysis of the optical photometric data obtained with the optical monitoring camera (OMC) on board INTEGRAL are presented. The major goal of this work was to classify the thousands of light curves obtained and to identify and study relevant scientific cases extracted from the large sample of data. In its 12 years of operations, OMC has observed a very large amount of classical variable sources, including pulsating stars, eclipsing binaries, rotating stars, AGN, etc. The compilation of the first catalog of optically variable sources observed by OMC, including information on their brightness, variability, periodicity, and object type classification, is presented. Within the sources in this catalog, a search for eclipsing binaries with one pulsating component has been carried out. One of the identified systems, DY Aqr, has been studied in detail. On the other hand, apart from these serendipitous observations, OMC was designed to provide optical monitoring of the sources observed by the main X- and gamma-ray instruments IBIS and JEM-X on board INTEGRAL. For the first time, simultaneous observations of the optical and X- and gamma-ray sky over more than 12 years are presented. In this thesis, two different works including multiwavelength information provided by INTEGRAL have been performed. In the first one the global properties of the emission of high-energy sources in different energy bands (hard X-rays, optical, IR, and MIR) have been studied. The emission from the different types of objects has been compared, looking for similarities and differences that could reveal information about the nature of their powerful sources. The second one consists of a multiwavelength long-term variability analysis, using light curves of the INTEGRAL instruments IBIS, JEM-X, and OMC, as well as from other highenergy missions and optical surveys, with a temporal coverage of more than 12 years.