The ACLS database provides citations for its e-books in the MLA, APA, or Chicago Styles that you can copy and paste onto your bibliography or Works Cited page. Once you've found a book you would like to cite, click on the "Read Book" button to open it. 
Click on the "Get Citation" button at the top of the screen to access the formatted citation.
Choose your citation style and click the "Copy Citation" button.
Paste the citation in your document or email to save.