Adams, Robert P. 2008. Junipers of the World: The Genus Juniperus. Second edition. Trafford Publishing.
Highly recommended. Brief versions of the descriptions, some of which are reproduced here at the Gymnosperm Database, are available online at Adam's website, www.juniperus.org, but they offer only a sampling of the wealth of information in this volume. Excerpts can be viewed and the book can be ordered from the publisher at www.trafford.com.