Think Tank Search searches the websites of institutions that generate public policy research, analysis, and activity. These sites are affiliated with universities, governments, advocacy groups, foundations, and non-governmental organizations. Inclusion is based upon the relevancy of subject area to HKS coursework and scholarship, the availability of the think tank’s research in full-text on the website, and the think tank’s reputation and influence upon policy making. The list represents a mixture of partisan and non-partisan think tanks.

Countries were mapped to regions based on the physical location of the think tank's headquarters and the UN's composition of macro geographical (continental) regions, geographical sub-regions, and selected economic and other groupings.

The Open Think Tank directory aims to pull together key information about policy organisations into one place. Today, it features public information for more than 3,600 organisations worldwide. The directory supports sector transparency and information accessibility.