Several of my books are available both as paperback and Kindle editions. My latest book, Selecting A Print-on-Demand Company: Comparing CreateSpace and Lightning Source for POD Self-Publishing is available in both a paperback and a Kindle edition.
With my real job taking up more time and my second child graduating from Texas A&M and obtaining her first job as a Civil Engineer (proud father moment!), I simply forgot to ask Amazon to link the two editions. The Publishing Maven gently reminded me I needed to do so.
Evidently the linking of the two helps the books come up higher in the Amazon search algorithm. Every author wants his or her book coming up as high as possible in the search results! Shame on me for not taking care of this.
As per The Publishing Maven's directions, if you have both a print and a Kindle edition and want them linked, send an e-mail to the Kindle Direct support team requesting the editions to be linked on Amazon. Use the Contact Us link on the bottom of your Kindle Direct page. Be sure to include the ISBN of the print editon and the ASIN of the Kindle edition. It will take a few days to link the two editions and for the reviews to match-up as well.
Be sure to list the books in your bibliography on your Author Central page as well. It takes less than a minute to do so.
Taking these steps are ethical ways to work the Amazon system to insure your book's best possible listing in Amazon's search results.