CLOCKSS (Controlled LOCKSS) is a collaborative endeavor between research libraries and leading academic publishers that provides what's known as a "dark archive" to help sustain access to web-based scholarly content. A dark archive is a repository that doesn't grant public access but preserves the information contained as needed. As such, the material is only available if a trigger event occurs, with the open-source LOCKSS technology checking the stored data on a regular basis to make sure it remains viable and valid. In other words, if web-based content being stored in the archive is in danger of disappearing, CLOCKSS will "trigger" it and make it accessible again. Trigger events so far have been rare, but the project's website provides information about what resources have been triggered over the life of the project. With 12 different archive nodes, the project preserves authoritative versions of some 46 million journal articles, 25,000 serial and 260,000 book titles, as well as other materials and metadata. As of this writing, CLOCKSS has 300 participating libraries and 400 participating publishers. The project aims to keep operating costs low and make it possible for any institution to participate. With sustainability in mind, should the project fold for any reason, 4 of the 12 library nodes have committed to continued preservation of the archive's content. Details about joining CLOCKSS, and more information about the benefits of joining, are available on the page linked above.