A composite stringer and skin structure, comprising: a polymer based elongated stringer having reinforcing fibres positioned in a plurality of adjacent layers, first and second layers of the reinforcing fibres being oriented at angles +δ and -δ relative to a selected reference direction, wherein |δ| is a first relatively shallow angle between zero degrees and twenty degrees, and third and fourth layers of the reinforcing fibres being oriented at angles +γ and -γ relative to the selected reference direction, wherein |γ| is a second relatively broad angle between forty-five and ninety degrees, the stringer being formed as a ply arrangement having one or more sets of first, second, third and fourth layer groups (72, 74, 76, 78) wherein each layer group (72, 74, 76, 78) includes five adjacent layers selected from the first layer, the second layer, the third layer and the fourth layer, and a polymer based and fiber reinforced skin member that adjoins the polymer based elongated stringer, characterized in that the structure further comprises an adhesive material interposed between the polymer based elongated stringer and the skin member, and in that: the first layer group comprises, in order, a first layer forming a first outer layer, a second layer, a third layer, a first layer, and a second layer forming a second outer layer and the second layer group comprises, in order, a first layer forming a first outer layer, a second layer, a fourth layer, a first layer, and a second layer forming a second outer layer and the third layer group includes, in order, a second layer forming a first outer layer, a first layer, a fourth layer, a second layer, and a first layer forming a second outer layer and the fourth layer group comprises, in order, a second layer forming a first outer layer, a first layer, a third layer, a second layer, and a first layer forming a second outer layer; and further wherein, in the polymer based elongated stringer, the second outer layer of the first layer group faces the first outer layer of the second layer group and the second outer layer of the second layer group faces the first outer layer of the third layer group and the second outer layer of the third layer group faces the first outer layer of the fourth layer group. a polymer based elongated stringer having reinforcing fibres positioned in a plurality of adjacent layers, first and second layers of the reinforcing fibres being oriented at angles +δ and -δ relative to a selected reference direction, wherein |δ| is a first relatively shallow angle between zero degrees and twenty degrees, and third and fourth layers of the reinforcing fibres being oriented at angles +γ and -γ relative to the selected reference direction, wherein |γ| is a second relatively broad angle between forty-five and ninety degrees, the stringer being formed as a ply arrangement having one or more sets of first, second, third and fourth layer groups (72, 74, 76, 78) wherein each layer group (72, 74, 76, 78) includes five adjacent layers selected from the first layer, the second layer, the third layer and the fourth layer, and a polymer based and fiber reinforced skin member that adjoins the polymer based elongated stringer, characterized in that the structure further comprises an adhesive material interposed between the polymer based elongated stringer and the skin member, and in that: the first layer group comprises, in order, a first layer forming a first outer layer, a second layer, a third layer, a first layer, and a second layer forming a second outer layer and the second layer group comprises, in order, a first layer forming a first outer layer, a second layer, a fourth layer, a first layer, and a second layer forming a second outer layer and the first layer group comprises, in order, a first layer forming a first outer layer, a second layer, a third layer, a first layer, and a second layer forming a second outer layer and the second layer group comprises, in order, a first layer forming a first outer layer, a second layer, a fourth layer, a first layer, and a second layer forming a second outer layer and the third layer group includes, in order, a second layer forming a first outer layer, a first layer, a fourth layer, a second layer, and a first layer forming a second outer layer and the fourth layer group comprises, in order, a second layer forming a first outer layer, a first layer, a third layer, a second layer, and a first layer forming a second outer layer; and further wherein, in the polymer based elongated stringer, the second outer layer of the first layer group faces the first outer layer of the second layer group and the second outer layer of the second layer group faces the first outer layer of the third layer group and the second outer layer of the third layer group faces the first outer layer of the fourth layer group.