"Think tank" refers to a policy institute or a research institute which conducts research on topics such as economics, political climate, military, social policy and culture. Well-known political think tanks include:
Searching the catalog for "united states" AND "immigration" can yield many helpful results. Searching by specific terms, including geographic area, period in time, thematic subject, and persons involved in an agreement may provide more insight into the process.
The Congressional Research Service, a division of the Library of Congress, provides policy and legal analysis to representatives and senators in Congress. CRS reports are renown for authoritative, objective, and non-partisan research but are not directly released to the public. CRS reports are available in several online collections including: