24 Association of Research Libraries Research Library Issues 302 — 2021 EPUB3 is now the predominant format for e-books. Originally developed as a project of the International Digital Publishing Forum in 2010, it is now a standard run out of the Web Accessibility Initiative. EPUB3 allows for multiple resources in a single file, using a specified reading order or another reading order. The current version is EPUB 3.2, which was approved and published by W3C as a Final Community Group Specification (slightly different from a standard) in 2019,16 however, earlier versions of EPUB were adopted as international technical standards by the International Organization for Standardization (ISO). EPUB3 was designed to be easy to make accessible, and over the past few years, there has been a major shift from publishers putting textbooks in PDF format, to instead publishing their books in EPUB3 format. Of the three formats for digital content described here, PDF format is considered to be the hardest format to make accessible. While HTML and EPUB3 were built with accessibility in mind from the start, the guidelines for creating accessible PDF content (known as PDF U/A, PDF Universal Access, or sometimes as the Matterhorn Protocol) were created long after the creation of the PDF format.17 While most web content development and management tools have some features built in to encourage accessibility, there are very limited tools available for making PDF files accessible, and they are often hard to use. The limitations in the existing tools have even caused some universities to try and limit or eliminate the PDF format from their campus (affectionately named the “Great PDF Purge” by North Carolina State University).18 This seems to be a valid concern, as some campus leaders were concerned that during the COVID-19 pandemic, their level of PDF accessibility on campus actually decreased, as paper forms were quickly scanned as graphical PDF files without considering accessibility.19 Until better tools and solutions are in place to assist with creating and remediating PDF files for accessibility, this will continue to be the hardest format to make accessible.