Gelli Plate Printing
book by Joan Bess

The book is written by the creator of the Gelli line so you know that she has a wealth of experience with these tools. She's the inventor! She talks about a wide range of topic, from setting up your creation area to cleaning up. She talks about all sorts of paint types and their pros and cons. She discusses the types of tools one can use - both bought and made.
And the art!
I'm confused by another reviewer who said there weren't any instructions in here. She provides fairly detailed instructions for a slew of design styles. She goes through using stamps and found objects. Through layering. Adding paint and subtracting it. Using Q-tips, straws, erasers, and combs. How to make your own tools. How to create cool effects by adding on drawings or clip art.
Yes, at the very end of the book there's a showcase of other artists' works and in that area there are only brief descriptions about how those artists came up with their end product. But that's only an add-on appendix to the book. The vast majority of the book is Joan's own instructions and work, done fairly step by step.
Here's one of her example pages.

Well recommended for someone who enjoys the feel of a book in hand, or the ability to sit down with friends and peruse the options together. Yes, the web has a wealth of information, but I'm a strong proponent of having a one-stop resource that is neatly organized when plowing at a new topic.
Well recommended.
Buy Gelli Plate Printing from Amazon.com
Printmaking Basics and Tips - main page