The following is taken from the website of the website of The Society of American Archivists 

What Are Archives and How Do They Differ from Libraries?

Libraries in towns (public libraries) or universities (academic libraries) can generally be defined as “collections of books and/or other print or nonprint materials organized and maintained for use.”* Patrons of those libraries can access materials at the library, via the Internet, or by checking them out for home use. Libraries exist to make their collections available to the people they serve.

Archives also exist to make their collections available to people, but differ from libraries in both the types of materials they hold, and the way materials are accessed.

• Types of Materials: Archives can hold both published and unpublished materials, and those materials can be in any format. Some examples are manuscripts, letters, photographs, moving image and sound materials, artwork, books, diaries, artifacts, and the digital equivalents of all of these things. Materials in an archives are often unique, specialized, or rare objects, meaning very few of them exist in the world, or they are the only ones of their kind.

  Examples of archival materials include: letters written by Abraham Lincoln (Abraham Lincoln Presidential Library and Museum, Springfield, Illinois), Frank Lloyd Wright’s architectural drawings (Avery Architectural and Fine Arts Library, Columbia University, New York), photographs documenting the construction of the Panama Canal (Transportation History Collection, University of Michigan Special Collections), and video footage from I Love Lucy television episodes (the Paley Center for Media, New York and Los Angeles).

• Access to Materials: Since materials in archival collections are unique, the people (archivists) in charge of caring for those materials strive to preserve them for use today, and for future generations of researchers. Archives have specific guidelines for how people may use collections (which will be discussed later in this guide) to protect the materials from physical damage and theft, keeping them and their content accessible for posterity.

  Example: Checking out a book from a library causes it to eventually wear out, and then the library buys a new copy of the same book. Checking out the handwritten diary of a historic figure from an archives would cause the same physical deterioration, but the diary is irreplaceable.

Note that there is a great deal of overlap between archives and libraries. An archives may have library as part of its name, or an archives may be a department within a library.

Example: The Performing Arts Reading Room in the Library of Congress.

^{*Joan M. Reitz, ODLIS – Online Dictionary for Library and Information Science (Libraries Unlimited, 2010), http://www.abc-clio.com/ODLIS/odlis_l.aspx.}