Abstract: A self-latching trailer coupler for use with a ballhead coupling post is disclosed. The coupler includes a housing having a forward portion that forms a receiving socket, and a rear portion. A latching member is disposed within the rear portion of the housing and is adapted for movement between a latched and a released position, the movement of the latch member being controllably guided along a complex path by guide pins and guide slots. The latching member has a socket which engages the ballhead when the coupler is positioned over a ballhead. Downward force on the coupler, as would be due to the load on the tongue of a trailer, automatically translates and rotates the latch member to a fully engaged locked position. A self-actuating locking device is provided for locking the latching member in its latched position. In connection with the locking device, a lever for releasing the locking device is also provided.