Abstract: A constructional toy including a plurality of main building blocks, preferably square and triangular in shape, all having identical grooves in their side faces, the mouth of each groove being narrower than the rest of the groove. The blocks are connected together by connecting elements each having a cross section in the shape of a symmetrical star having 2N points, where N is at least three. Each connecting element is a sliding fit in the grooves in the main blocks, with N adjacent points of its star-shaped cross section trapped in the groove and the other N points outside the groove, thus enabling the blocks to be connected together side face to side face.