The New England Historic Genealogical Society (NEHGS) was founded in 1845 and has an immense collection of genealogical resources. New England is undoubtedly its strength, but it has a considerable collection from other locales. The more likely New Englanders were to be concerned about the area, the greater the likelihood of resources (i.e. New York, Ohio, England, and the colonial South all have relatively strong collections; less so the American west and any other country).
There are two primary resources for the public: the library and the website. Membership ($75/year/$90/family and up) is generally required to access the website resources, but non-members can use the library for a daily fee of $15.
Located on Boylston Street in Boston. Open to members and the public Tuesdays through Saturdays.
Description from their website: The NEHGS Research Library offers a comprehensive collection of more than 200,000 books, periodicals, and microform materials, as well as over one million manuscripts. Its book holdings include nearly all published New England genealogies, local histories, and related periodicals. Its microtext collection, with more than 40,000 items, contains copies of the original town, probate, land, and vital records; city directories; censuses; and immigration records for most of New England and eastern Canada. Beyond New England, family researchers will find many important published and primary sources for other regions, including U.S. states beyond New England, England, Ireland, Scotland, Germany, eastern Canada, French Canada, Europe, and Australia.
An additional important resource at the library are the librarians, most of whom have extensive research experience, and can help direct patrons struggling with brick walls.
See also their library guide.
A portion of their library is available for lending by mail to members.
Many NEHGS-published or out of copyright New England resources are being put online at the Society's website. See Repository:AmericanAncestors.org. (Materials available in hard copy should link to this repository. Materials that have been put online should link to the website.)