As the United States and Europe look for additional sources of leverage in Pakistan and Afghanistan, a heightened role for China is one of the most promising-and the least discussed. China's substantial strategic interests in Pakistan, its major investments in both countries, and security concerns that range from narcotics flows to terrorist bases give it many shared stakes with the West.

But translating common interests into complementary policies will be a challenge. While Beijing is willing to expand cooperation with the Obama administration on Af-Pak, it is concerned to protect its close relationship with Islamabad and has broader anxieties about NATO's role in the region. If China is going to be brought on board as an effective partner, the United States and Europe must develop a carefully focused engagement strategy that takes full account of both the difficulties and the opportunities that greater Chinese involvement presents.