Since purchasing a house, I've been trying to learn more about organic gardening, thus reading a number of books to help get a handle on the concepts and techniques. I originally checked this out from the library and liked it so much I bought it. There are probably more complete books on the subject, but this is a good general guide for beginner's.
The "21st Century" portion of the title implies that this is putting forth something new or innovative, which isn't quite the case, but that shouldn't deter anyone from reading. The section on composting actually describes (in detail) how to make cold vs. hot compost pile, and there are instructions for making compost/manure tea, creating a worm bin, double-digging, crop rotation, etc. I especially like the index of fruits and vegetables, with 1-2 page long descriptions that are helpful for the beginning gardener. Well organized and easy to read.
Some criticisms that don't detract from the overall quality. Virtually NO information on flower gardening--even less than the Rodale Illustrated Encyclopedia. The section on double-digging implies that it is a necessity for the organic vegetable garden, which it is not (other sources suggest that it is most useful for sustainable farming in regions with poor soil quality, i.e. not the Midwest). There are sections that could be fleshed out more, specifically the pests and diseases, but there is enough it doesn't feel completely lacking.
As a beginning organic gardener, I got more out of this book than the equally general Rodale Illustrated Encyclopedia. The compost section especially, gave me a strong starting point. Recommended.