Nowadays, you can find free and publicly available open educational resources and open textbooks on a variety of subjects. Many of these are licensed in ways that allow for remixing (more on this later).
Quite a few open textbooks have been built on Pressbooks, where the underlying software makes them extra easy to remix if you also have a Pressbooks network.
Here are a few places to start your search for openly licensed textbooks and course materials that you might adapt:
Open Textbook Library
The Open Textbook Network maintains the Open Textbook Library. It contains texts that have undergone review by faculty in higher ed and are either in use at “multiple higher education institutions or affiliated with an institution, scholarly society, or professional organization.” You can download the books from the library free of charge or print them at low cost. Often, the entries will point to the Pressbooks webbook of the books, where you may be able to download XML and other formats, as well.
MERLOT is a project of the California State University system that indexes a variety of open educational resources, including 5,800 open textbooks plus associated course materials. You can search by subject or search for related course materials by searching a book’s ISBN.
BCcampus OpenEd offers a repository of open textbooks from BCcampus as well as other institutions, and allows you to find, adopt or adapt open textbooks. BCcampus uses Pressbooks for faculty-created open textbooks, so it also offers a variety of Pressbooks guides, training, and help for authors using Pressbooks to create their OER.
Rebus Community supports open textbook creation through a collaborative workflow platform and community, which make it easy for faculty to collaborate globally on open textbook projects. They use Pressbooks as their book formatting engine and have project-managed a growing number of open textbooks. [SOON: You can view their catalog at https://press.rebus.community/].
OpenStax produces openly licensed textbooks using a traditional publishing workflow. They offer a library of open textbooks that you can download and adopt from their website and remix. Pressbooks will soon have a plugin that will make it easy to import content from OpenStax into Pressbooks.
Pressbooks networks: A variety of universities with growing open textbook programs have their own Pressbooks systems. You may stumble across a link to a book you’d like to adopt on one of their systems. Pressbooks webbooks usually show the book license on the home page and sometimes also showcase other file formats that you can download.
Once you’ve found some resources you like, it’s important to determine what rights the license allows.