Abstract: The invention relates to a device for automatically joining and machining assemblies consisting of several components each and retained on a work-piece carrier (4) in a transfer line with retoolable machining stations (3). In the machining station (3), the assembly components are first taken off the workpiece carrier, brought into the joining position relative to each other, retained there and machined, in particular tacked or finish-welded. To carry out these various activities and to make the machining station highly flexible, the latter has several tool carriers (22, 23) which can move in at least three axes. The tool carriers (22, 23) are each disposed in a parallel plane above or below the workpiece carrier (4) so they can travel freely. The tool carriers (22, 23) support individual tools which they can change automatically at stationary or movable tool magazines (31, 33, 34).