Background: An accurate description of the initial and final state interactions in the 18O+76Se collision is demanded by the NUMEN project. The study of single and double charge exchange nuclear reactions is the main purpose for NUMEN, since these can be used as tools to provide experimentally driven information about nuclear matrix elements of interest in the context of neutrinoless double-?? decay. To date, the details of the optical potentials and nuclear response to isospin operators for many of the projectile-target systems proposed for the NUMEN double charge exchange studies are poorly known. The 18O+76Se case, here under study, is particularly relevant due to its connection with the 76Ge neutrinoless double-?? decay. Purpose: In this work the authors want to characterize the initial-state interaction for the 18O+76Se reactions at 275 MeV incident energy determining the optical potential and evaluating the effect of couplings with the inelastic scattering on the elastic channel. Methods: The angular distributions of differential cross section were measured in the angular region between 4??? and 22??? in the center-of-mass reference frame. The cross sections were compared with theoretical calculations, that adopt different optical potentials. Coupling effects on the elastic channel were determined into the coupled channels formalism. Results: The excitation energy spectrum of the colliding nuclei and the cross section angular distributions were measured with satisfactory energy resolution. The elastic scattering cross section is not well reproduced in the full angular range explored when the optical model approach is adopted. A good agreement is found using coupled channel calculations. The initial state interaction for the 18O+76Se nuclear reactions at 275 MeV is determined. Conclusions: Coupled channels effects are crucial to obtain a good description of the measured elastic and inelastic channels cross sections, even at large transferred momenta where the optical model approach fails in reproducing the experimental data. The role of channel coupling could be relevant also in the analysis of other open reaction channels in the same collision and should be accounted for in double charge exchange analyses as well.Funda????o de Amparo ?? Pesquisa do Estado de S??o Paulo (FAPESP)Instituto Nacional de Ci??ncia e Tecnologia - F??sica Nuclear e Aplica????es (INCT-FNA)FAPESP: 19/07767-1INCT-FNA: 464898/2014-5