Before revision:  We will prove that for euclidean Traveling Salesman Problems with n cities the approximation ratio of the 2-Opt heuristic is \Theta(\log n/ \log \log n).  ] 
After revision:  We will prove that for euclidean Traveling Salesman Problems with n cities the approximation ratio of the 2-Opt heuristic is \Theta(\log n/ \log \log n). This improves the upper bound of O(\log n) given by Chandra, Karloff, and Tovey ]