A modular alignment system has been designed and built at the Institut d'Astrophysique, Lige. Based on the multiple-beam autocollimation principle, it is composed of two collimators, a series of beam splitters and mirrors and a large reference flat. All the generated laser beams are aligned with respect to the latter and are projected onto corresponding test mirrors. These can then be set perpendicular to the beams by shimming the payload on which they are attached. The autocollimation is controlled visually by a micrometer stage, or on a TV screen. Some twenty beams may be aligned simultaneously with a precision of the order of one second of arc, regardless of the floor stability.