Think tanks are not government agencies, but they typically comment on, and seek to influence, public policy, so I've included info on them in this guide.
A think tank is an interdisciplinary body of experts such as scholars or former politicians that crafts opinions on regional, national or international policy and strategic direction, typically related to areas such as commerce, the military, immigration or social welfare. Often independent, some think tanks are known for certain political leanings and their reports and findings are interpreted accordingly.
Yusufali, Sasha. "Think Tank" in Canadian Encyclopedia.