Erin Sullivan's book, Retrograde Planets, was a landmark of sorts in astrology at the time it was first published in 1992. It was the first user-friendly astrology text/book to really address the issue of retrogrades in an in-depth and thought-full manner. Retrograde planets seem to turn around and go backward from our perspective on earth. During their backwards transit, they encourage us to look at the "under" or "other" side of things, thus the title of my review. We are all used to Mercury's retrograde three times a year, or we should be or at least have heard of it. Sullivan's book doesn't stop there. She considers the nature and mechanics of retrogression as it affects the planets Mercury, Venus, Mars, Jupiter and the outer planets as well. You will not find a more thorough or READABLE explanation of this important phenomena. Sullivan also gives a good long chapter to retrograde natal planets and the secondary progression of retrograde planets or planets to retrograde. Not the most exciting writer in the world, Sullivan is nonetheless, thorough, methodical, devoted to her work and readable enough. I give this 5 stars not because the book is a real can't put downer, but rather because Sullivan is a meticulous astrologer who really knows her stuff. "Retrograde Planets" should be considered a good intermediate reference volume for the budding professional astrology.