Collection of resources by the U.S. Citizenship and Immigration Services branch of the federal government. These include resources about as well as a link to the application for U.S. Citizenship. There are practice test and study materials available.
From the website, "Many community organizations and social service providers offer citizenship classes and assistance with the naturalization process."
Preparing for the Oath resource provides materials to learn and practice for the U.S. Naturalization Test. It is a resource cocreated by several government organizations.
Books
The following resources are PSC Library's collection of books and eBooks on citizenship.