Electronic books may include books found on personal websites, databases, or even in audio form. Use the following format if the book you are using is only provided in a digital format or is difficult to find in print. If the work is not directly available online or must be purchased, use "Available from," rather than "Retrieved from," and point readers to where they can find it. For books available in print form and electronic form, include the publish date in parentheses after the author's name. For references to e-book editions, be sure to include the type and version of e-book you are referencing (., "[Kindle DX version]"). If DOIs are available, provide them at the end of the reference.