Abstract: A Rotating Flexible Wing Power System for extracting low-cost electricity and mechanical energy from moving fluids including wind and water currents. The Rotating Flexible Wing Power System generally includes a single long curved flexible wing supported at its ends so that it can rotate or swing around a longitudinal axis that intersects the endpoints of the wing. Rotation mechanisms are located at each end of the wing allowing the wing to rotate freely about its longitudinal axis. Lift forces on the wing resulting from the moving fluid cause the wing to start and continue rotating. These lift forces also create oscillating longitudinal forces in the flexible wing which move the ends of the flexible wing towards and away from each other. This movement may be harnessed to drive a generator or pumping device connected to the flexible wing. One or both ends of the wing can be connected to tethers so that the overall length of the flexible wing is increased.