This collection of declassified analytic monographs and reference aids, designated within the Central Intelligence Agency (CIA) Directorate of Intelligence (DI) as the CAESAR, ESAU, and POLO series, highlights the CIA's efforts from the 1950s through the mid-1970s to pursue in-depth research on Soviet and Chinese internal politics and Sino-Soviet relations. The documents reflect the views of seasoned analysts who had followed closely their special areas of research and whose views were shaped in often heated debate. Continuing public interest in the series, as reflected in numerous requests through Freedom of Information and Executive Order channels, led CIA's Office of Information Management Services (IMS) to conduct a search of Directorate of Intelligence record systems for documents in this series and then undertake a declassification review of all the documents we located. The 147 documents in this collection, amounting to over 11,000 pages of analysis, were written between 1953 and 1973. The collection includes a large number of newly declassified monographs as well as some studies that have been previously declassified and released to individual requesters. The continuing sensitivity of some documents in the series required that they be withheld from declassification.