A wind turbine blade extending in a spanwise direction between a root end and a tip end, and extending in a chordwise direction between a leading edge and a trailing edge, the blade having a pressure side and a suction side, and a trailing edge flap, the trailing edge flap comprising: a flap part protruding from the trailing edge on the pressure side of the blade, the flap part having a first section and a second section each having an upstream surface (72, 74) arranged to face an oncoming airflow in use; the first section extending from the trailing edge and having a proximal end and a distal end in cross-section, with the proximal end being located at or near the trailing edge and the distal end being spaced apart from the trailing edge; wherein the first section is oriented such that an obtuse angle is defined between the upstream surface of the first section and a plane that extends parallel to the local chordal plane and intersects the proximal end of the first section; the second section is oriented such that the upstream surfaces of the first and second sections (72, 74) together define a concave profile in cross section, the second section extending from the distal end of the first section and in an upstream direction; the second section has a proximal end and a distal end in cross-section, the proximal end of the second section adjoining, directly or indirectly, the distal end of the first section, and the proximal end of the second section being located downstream of the distal end of the second section in use; characterized in that the trailing edge flap is arranged on a transition portion of the blade between the root of the blade and a maximum chord of the blade; and the trailing edge flap further comprises a mount via which the trailing edge flap is attached to the blade, and wherein the flap part projects from the mount. a flap part protruding from the trailing edge on the pressure side of the blade, the flap part having a first section and a second section each having an upstream surface (72, 74) arranged to face an oncoming airflow in use; the first section extending from the trailing edge and having a proximal end and a distal end in cross-section, with the proximal end being located at or near the trailing edge and the distal end being spaced apart from the trailing edge; wherein the first section is oriented such that an obtuse angle is defined between the upstream surface of the first section and a plane that extends parallel to the local chordal plane and intersects the proximal end of the first section; the second section is oriented such that the upstream surfaces of the first and second sections (72, 74) together define a concave profile in cross section, the second section extending from the distal end of the first section and in an upstream direction; the second section has a proximal end and a distal end in cross-section, the proximal end of the second section adjoining, directly or indirectly, the distal end of the first section, and the proximal end of the second section being located downstream of the distal end of the second section in use; characterized in that the trailing edge flap is arranged on a transition portion of the blade between the root of the blade and a maximum chord of the blade; and the trailing edge flap further comprises a mount via which the trailing edge flap is attached to the blade, and wherein the flap part projects from the mount.