The forerunner of the OECD was the Organisation for European Economic Co-operation (OEEC), which was formed to administer American and Canadian aid under the Marshall Plan for the reconstruction of Europe after World War II.
The Convention transforming the OEEC into the OECD was signed at the Chateau de la Muette in Paris on 14 December 1960 and entered into force on 30 September 1961.
Since then, the OECD's vocation has been to deliver greater well-being worldwide by advising governments on policies that support resilient, inclusive and sustainable growth. Through evidence-based policy analysis and recommendations, standards and global policy networks, including close collaboration with the G7 and the G20, the OECD has helped advance reforms and multilateral solutions to global challenges. These span the public policy horizon, from the polluter pays principle, which the OECD developed in the 1970s, to PISA in education, not to mention tax transparency and artificial intelligence. Throughout its history, the OECD has striven to become more global, more inclusive and more relevant.
source : OECD, https://www.oecd.org/60-years/