The fox, the rabbit, and the lettuce

Question: A merchant has a fox, a rabbit, and a head of lettuce and sits on the edge of a river. He has a small raft capable of carrying only himself and one item at a time, but without his supervision the fox will eat the rabbit, and the rabbit will eat the lettuce. How can he successfuly transport all goods from one side of the river to the next without losing the lettuce or rabbit? The dilemma, of course, is true regardless of which side of the river they are on and there is no other way across.