Note that the 2019 Global Go To Think Tank Report has a change from previous indexes. Any think tank that has ranked as the top think tank in a category for three consecutive years will not be included in the ranking list for the next three years; instead, it will be given a unique distinction: "Think Tank Center of Excellence." This year, the Brookings Institution (U.S.) received this distinction. Read more about this new classification on page 57 of the 2019 Global Go To Think Tank Report.
For the combined rankings of the top 176 think tanks worldwide (US and non-US), consult pages 65-71 of the 2019 Global Go To Think Tanks Report. Links to all organizations mentioned are available in the appropriate regional lists.