University of Chicago Press style guide for American English grammar and usage and for preparation of documents for publishing.
Electronic books are cited exactly as their print counterparts with the addition of a media marker at the end of the citation: Kindle edition, PDF e-book, Microsoft Reader e-book, Palm e-book, CD-ROM, etc. Books consulted online are also cited exactly as their print counterparts with the addition of a DOI (or URL) at the end of the citation. Stable page numbers are not always available in electronic formats; therefore, you may, instead, include the number of chapter, section, or other easily recognizable locator.
** Note: This guide demonstrates basic features of CMS, but there are two types of CMS styles. The Notes-Bibliography System (NB) is used by those in literature, history, and the arts. The other documentation style, the Author-Date System, is nearly identical in content but slightly different in form and is preferred in the social/sciences. Please see the OWL guide for more details.
The 2nd example is an ebook. 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.