1. The Digital Negative: Raw Image Processing in Lightroom, Camera Raw, and Photoshop (2nd Edition) by Jeff Schewe
2. The Adobe Photoshop Lightroom CC Book for Digital Photographers by Scott Kelby
3. Adobe Photoshop Lightroom CC (2015 release) / Lightroom 6 Classroom in a Book (Adobe Press)
4. The Adobe Photoshop Lightroom CC / Lightroom 6 Book: The Complete Guide for Photographers by Martin Evening
Some books are not published yet, so you can advise them based on your experiences with the earlier editions.
Thanks a lot.
Thanks Paige ...
I want to buy only one book.
Which one would you advise most?
That depends on what you really want to learn the most.
If you want to learn Developing, it's Schewe. If you want to learn organizing, it's The DAM Book. If you want a good overall book that covers the entire program called LR CC/LR 6, then its Evening.