"With over 1,000 different archival institutions represented, ArchiveGrid helps researchers looking for primary source materials held in archives, libraries, museums and historical societies."
DPLA brings together the riches of Americaβs libraries, archives, and museums, and makes them freely available to the world. Includes many primary sources and other public domain materials.
HathiTrust is a partnership of academic & research institutions, offering a collection of millions of titles digitized from libraries around the world.
The Internet Archive provides access to primary sources in the public domain. Metadata is of uneven quality, so make use of phrasal searching when possible.