When using HTML and related technologies to produce books and other print output, the question of pagination must be considered. This includes page counters, repeated elements in headers and footers, as well as mechanisms to avoid awkward page breaks. Paged.js is an open-source library that implements a series of polyfills for the Paged Media and Generated Content for Paged Media CSS modules. It is still experimental but fills an important gap in the "write once, publish everywhere" story for HTML.