A fifth wheel coupling (4) for coupling a tractor (2) and a semi-trailer (3) of a tractor-trailer unit (1) comprises a coupling device arranged on the tractor (2) for receiving and arresting a king journal fastened to the semi-trailer (3). In order to achieve the best possible swiveling properties at a design of low complexity, there is provided as a fifth wheel coupling a ball-shape coupling (4) with a coupling ball (5) and an associated holding-down device (6) on the one hand and a ball cup (7) enclosing the coupling ball (5) in the coupling position and the attached butt part (8) on the other hand, with the coupling ball (5) and the holding-down device (6) replacing the coupling device and the ball cup (7) and the butt part (8) replacing the king journal.