For the non-academics on my list, this means that bitonal images of (nearly) every book printed for the English market before 1800 is now available online, for free, on archive dot org.
(Short thread w/history of this massive early twentieth-century undertaking.)
The English Short Title Catalogue (like its German counterparts) was part of post-World Wars awareness of the fragility of cultural heritage AND the new availability of microfilm technologies.