A multi layer composite L-shaped stringer for use in an aerospace structure comprises a foot and a web extending from an edge of the foot. A first surface on the foot is shaped to abut a structure to be stiffened. The foot also has a second surface opposite the first surface. The web has a third surface and a fourth surface at the same layer in the composite material as the first and third surfaces, respectively. The geometry of the stringer may vary along its length (L) so that as the first surface is displaced towards the second surface, the fourth surface is displaced towards the third surface. The developed width (DW) from the distal edge of the foot to the distal edge of the web of the stringer may be substantially constant for all cross-sections along a length of the stringer. The risk of causing, during fabrication of the stringer, undesirable creasing, stressing or stretching of composite material layers in a region in which the geometry of the stringer varies may be reduced by means of such arrangements.