Abstract: A locking device for use on valves such as ball valves having a body and a rotatable handle on the body comprises a first body half, a second body half, and a hinge pivotally connecting the first and second body halves together such that the locking device is positionable in open and closed positions on the valve. A body opening is formed in the first and second body halves to receive the valve body in the closed position. First and second handle openings are formed in the first and second body halves to receive the valve handle, and substantially prevent the handle from being rotated, in respective first and second positions of the handle. The handle is externally visible in both positions. A locking mechanism is provided on the first and second body halves to retain the locking device in the closed position. A lock can be used to prevent the locking device from being removed from the valve without permanently damaging the locking device.