The out-of-plane seismic response of historic stone masonry walls is investigated herein, with due consideration to soil–foundation–structure interaction (SFSI). A series of pushover tests were performed on reduced scale (1:3) wall specimens, which consisted of a three-leaf stone masonry built on top of a spread footing. The walls were subjected to out-of-plane displacement, imposed at mid-height. Initially, a set of experiments were conducted ignoring SFSI. Then, the specimens were founded on a sand layer to examine the role of SFSI. Two idealized soil deposits were modelled: (a) dense sand of relative density D_r = 92%, and (b) loose sand of relative density D_r = 33%. It is shown that the performance of the walls is substantially affected by SFSI effects, as well as by the boundary conditions.