Drawing on a wealth of new sources, this work documents the evolving relationship between Moscow and Peking in the twentieth century. Using newly available Russian and Chinese archival documents, memoirs written in the 1980s and 1990s, and interviews with high-ranking Soviet and Chinese eyewitnesses, the book provides the basis for a new interpretation of this relationship and a glimpse of previously unknown events that shaped the Sino-Soviet alliance. An appendix contains translated Chinese and Soviet documents - many of which are being published for the first time. The book focuses mainly on Communist China's relationship with Moscow after the conclusion of the treaty between the Soviet Union and Kuomingtang China in 1945, up until the signing of the treaty between Moscow and the Chinese Communist Party in 1950. It also looks at China's relationship with Moscow from 1920 to 1945, as well as developments from 1950 to the present. The author reevaluates existing sources and literature on the topic, and demonstrates that the alliance was reached despite disagreements and distrust on both sides and was not an inevitable conclusion. He also shows that the relationship between the two Communist parties was based on national interest politics, and not on similar ideological convictions.