A device for the generation of electrical power from a fluid flow, and more particularly for harvesting power from flows downhole in oil or gas wells, comprises a cylinder or other blunt body (1) arranged crosswise to the flow and supported on the end of a sprung cantilever arm (3) held in a fixed mount, with freedom to oscillate in response to the shedding of a Karman vortex trail v from the' body. The resultant motion of the body (1) and arm (3) is converted into electrical energy by piezoelectric material (5) which is attached to, and stressed by, flexure of the arm. Other arrangements of piezoelectric and inductive power generation from the oscillation of the device are described.