1500s: PPP concept is first used at the University of Salamanca in Spain
1918: Swedish economist Gustav Cassel develops a modern definition of PPP.
1940: British economist Colin Clark deduces concept of PPPs to estimate levels of real income.
1950s: The Organization for European Economic Cooperation carried out an experimental international price and volume comparison of GDP in nine European economies and the United States.
1960s: The Economic Commission for Latin America uses PPP-based comparisons of real products in 19 Latin American economies; the Council for Mutual Economic Assistance uses PPP-based comparisons of national income between several central and eastern European centrally-planned economies; the Conference of European Statisticians approves PPP-based comparisons of consumption levels among small groups of market and centrally-planned economies.
1968: The United Nations Statistics Division (UNSD) and the International Comparisons Unit of the University of Pennsylvania led by Irving Kravis, Alan Heston and Robert Summers establish International Comparison Project on the recommendation of the United Nations Statistical Commission (UNSC). The ICP begins as a research project with financial contributions from Ford Foundation and the World Bank. The goal is to set up a regular program of worldwide, PPP-based comparisons of GDP.
1970: ICP Phase I. For 10 economies (reference year 1970).
1973: ICP Phase II. For 16 economies (reference year 1973).
1975: ICP Phase III. For 34 economies (reference year 1975). First official EU comparison covering all 9 member states is also conducted.
1979: The European Comparison Programme is launched under the European Commission of Europe. It covers European and non-European OECD countries. The first comparison is set for year 1980.
1980: ICP Phase IV. For 60 economies (reference year 1980). The ICP discards its research status and becomes a regular part of the UNSD work program, with advice on methodology from the University of Pennsylvania.
1985: ICP Phase V. For 64 economies (reference year 1985).
1988: The University of Pennsylvania introduces Penn World Table and extends estimates of real GDP across countries and over time, starting from 1950.
1990: The International Comparison Project is renamed the International Comparison Program.
1993: ICP Phase VI: For 115 economies (reference year 1993). PPP-based regional comparisons also conducted. (ICP 1993 Global Report)
1997: A review of the OECD-Eurostat PPP Programme is conducted (The Castle Report).
1999: The UNSC evaluates the ICP (The Ryten Report) and considers launching the ICP with better management and more resources at global, regional and national levels.
2002: The World Bank conducts successful fund-raising efforts, and the UNSC agrees to a new ICP round in its 33rd session.
2003: The UNSC, at its 34th session, launches the ICP for reference year 2005, referred to as ICP 2005 round. The ICP Global Office is established at the World Bank.
2005: 146 economies conduct ICP 2005 round activities (reference year 2005).
2007: Global results produced for ICP 2005 round. (ICP 2005 Global Report)
2008: Friends of the Chair group evaluates ICP 2005 and recommends 2011 as the reference year for the next ICP round. (2008 Friends of the Chair Report on ICP)
2009: The UNSC , at its 40th session, launches ICP 2011 round.
2011: 199 economies conduct ICP 2011 round activities (reference year 2011).
2014: Global results produced for ICP 2011 round. (ICP 2011 Global Report)
2015: Friends of the Chair group evaluates ICP 2011 round. (2015 Friends of the Chair Report on ICP)
2016: Friends of the Chair group recommends more frequent ICP cycles, and the UNSC, at its 47th session, endorses the ICP as a permanent global statistical program.
2017: ICP stakeholders begin implementation of the 2017 cycle of the permanent ICP.