Abstract: A prefabricated expansion joint for a concrete slab, the joint comprising a hollow extrusion of plastics material having an enlarged base portion for connecting directly or indirectly to a surface on which a concrete slab is to be made, a top portion for coming flush with the surface of the concrete slab that is to be made, and an intermediate portion with two side walls extending between the base portion and the top portion. The top portion comprises a strip of flexible plastics material in which there extends a central web of relatively rigid plastics material connected via its bottom edge to the side walls of the joint, forming a single part together therewith and extending vertically over at least the major fraction of the height of the top portion of the joint.