This forum includes six commentaries on Lorenz M. Lüthi's book The Sino-Soviet Split: Cold War in the Communist World, published by Princeton University Press in 2008. Drawing on recently declassified documents and memoirs from numerous countries, Lüthi explains how and why the close alliance between the Soviet Union and the People's Republic of China fell apart in a remarkably short time, dissolving into fierce mutual enmity. Amassing a wealth of evidence, Lüthi stresses the role of ideology in the split, lending support to the arguments put forth nearly five decades ago by analysts like Donald Zagoria in his pioneering book on the Sino-Soviet rift. Six leading experts on Chinese foreign policy and Sino-Soviet relations discuss the strengths of Lüthi's book but also raise questions about some interpretations and omissions. The forum includes Lüthi's reply to the commentaries.