An anchor rope lock that locks the rope in response to tension exerted by the anchor, and that unlocks the rope for retrieval or adjustment in response to tension applied to the free end. A locking shoe is mounted on a horizontal pivot axis for pivoting towards locked and unlocked positions. The rope passes under a lower surface of the shoe and upwardly through a passage in a projecting toe portion. As the shoe pivots towards the locked position, the lower surface of the shoe moves towards the upper surface of an underlying base plate so as to compress the rope, and the passage in the toe of the shoe moves towards a vertical orientation so as to force the rope into a bend so that the anchor rope is held firmly at a fixed length. When reverse tension is applied to pivot the shoe towards the unlocked position, the lower surface of the shoe moves away from the surface of the base plate so as to release the rope and the passage in the toe portion moves towards a horizontal orientation so as to straighten the bend, so that the rope can be selectively retracted or extended through the lock assembly. From the shoe, the rope exits the top of the toe portion and is directed over a fairlead towards the anchor end. The greatest part of the weight of the shoe is located on the side of the pivot axis opposite the toe portion, so that the weight urges the shoe towards the locked position.