A method of making an elongate reinforcing structure for a wind turbine blade, the reinforcing structure comprising a longitudinally-extending web and a longitudinally-extending flange, the flange extending along a longitudinal edge of the web and being arranged transversely to the web, and the method comprising: providing a longitudinally-extending mould tool (120, 160, 180, 202, 214) having a mould surface (118, 162, 184, 204) bound by a first longitudinal edge (122, 190) of the mould tool (120, 160, 180, 202, 214), the mould surface (118, 162, 184, 204) being shaped to define the web of the reinforcing structure; providing a pultruded flange structure (134, 134a-g) comprising a flange portion (112, 112a-g) and a projecting portion that extends along the length of the flange portion (112, 112a-g) and projects transversely from a surface of the flange portion (112, 112a-g); supporting one or more first laminate layers of the web on the mould surface (118, 162, 184, 204); positioning the flange structure (134, 134a-g) adjacent to the first longitudinal edge (122, 190) of the mould tool (120, 160, 180, 202, 214) such that the projecting portion of the flange structure (134, 134a-g) overlies a first longitudinal edge region of the one or more first laminate layers and such that the flange portion (112, 112a-g) is transverse to the mould surface (118, 162, 184, 204); arranging one or more second laminate layers on top of the one or more first laminate layers such that the one or more second laminate layers at least partially cover the projecting portion of the flange structure (134, 134a-g); and integrating the one or more first laminate layers, the one or more second laminate layers and the projecting portion of the flange structure (134, 134a-g) in the mould (120, 160, 180, 202, 214) by means of a matrix material and thereby bonding the projecting portion between the one or more first laminate layers and the one or more second laminate layers. providing a longitudinally-extending mould tool (120, 160, 180, 202, 214) having a mould surface (118, 162, 184, 204) bound by a first longitudinal edge (122, 190) of the mould tool (120, 160, 180, 202, 214), the mould surface (118, 162, 184, 204) being shaped to define the web of the reinforcing structure; providing a pultruded flange structure (134, 134a-g) comprising a flange portion (112, 112a-g) and a projecting portion that extends along the length of the flange portion (112, 112a-g) and projects transversely from a surface of the flange portion (112, 112a-g); supporting one or more first laminate layers of the web on the mould surface (118, 162, 184, 204); positioning the flange structure (134, 134a-g) adjacent to the first longitudinal edge (122, 190) of the mould tool (120, 160, 180, 202, 214) such that the projecting portion of the flange structure (134, 134a-g) overlies a first longitudinal edge region of the one or more first laminate layers and such that the flange portion (112, 112a-g) is transverse to the mould surface (118, 162, 184, 204); arranging one or more second laminate layers on top of the one or more first laminate layers such that the one or more second laminate layers at least partially cover the projecting portion of the flange structure (134, 134a-g); and integrating the one or more first laminate layers, the one or more second laminate layers and the projecting portion of the flange structure (134, 134a-g) in the mould (120, 160, 180, 202, 214) by means of a matrix material and thereby bonding the projecting portion between the one or more first laminate layers and the one or more second laminate layers.