The Dark Tower is an incomplete manuscript written by C. S. Lewis that appears to be an unfinished sequel to the science fiction novel Out of the Silent Planet, though allegations have been raised about its authenticity. Perelandra instead became the second book of Lewis' Space Trilogy, concluded by That Hideous Strength. Walter Hooper, Lewis' literary executor, titled the fragment and published it in the 1977 collection The Dark Tower and Other Stories. The Lewis scholar Kathryn Lindskoog challenged the authenticity of the work.

Cambridge University Library is the main research library of the University of Cambridge. It is the largest of over 100 libraries within the university. The library is a major scholarly resource for members of the University of Cambridge and external researchers. It is often referred to within the university as the UL. Thirty-three faculty and departmental libraries are associated with the University Library for the purpose of central governance and administration, forming "Cambridge University Libraries".