Abstract The solution of the problem of the diffraction of an arbitrary acoustic wave by a block (including the spatial case) is considered. The same approach is used as in the case of diffraction by a wedge . The problem of diffraction by a block has been considered in many publications [2–6]. However, the most detailed solution has only been written out for the first of the diffraction waves which arise at the corners of the block. When the subsequent waves (or the incidence of non-planar waves) is considered, the solution obtained using both Green's functions as well as a radial expansion  is quite complicated. The results which are closest to those in this paper were obtained in  for the two-dimensional case.