The International Comparison Program (ICP) is a worldwide statistical initiative-the largest in geographical scope, in implementation time frame, and in institutional partnership. It estimates purchasing power parities (PPPs) for use as currency converters to compare the size and price levels of economies around the world. Numerous methodological improvements and operational guidelines were introduced in the 2011 round of the ICP for the advancement of the program. The Operational Guidelines and Procedures for Measuring the Real Size of the World Economy is a compilation of ICP operational guidelines and material prepared by the ICP 2011 Global Office team, consultants, and international experts. It describes the approach to and data requirements for the main price survey and special surveys, including the various guidelines produced and survey forms. It also covers the framework and requirements for national accounts activities for the ICP. In addition, this guide describes the procedures followed for data validation, computation of national annual averages, calculation of PPPs, aggregation, and linking. Disclosure of the procedures underlying the ICP 2011 process heightens the transparency of the program and allows interested stakeholders and users of the results to delve into the ICP methods and operational aspects in order to better understand and interpret the results.