title_body: Can EPUB 3.0 be viewed on EPUB 2 devices
upvoted_answer: The IDPF states the following in a thread about EPUB 3 Rendering in EPUB 2 reading systems
  
  
    Although EPUB 3 is not perfectly backwards compatible with EPUB 2, a goal of the recent revision was to ensure, as much as possible, a basic level of rendering when features overlap.
  
  
  The thread particularly mentions that providing the NCX data is necessary, which has been superseded with EPUB Navigation Documents
  as described in the EPUB 3 changes document
  
  So, if some care is taken, EPUB 3 files can be made to render on EPUB 2 reading systems.