The first decade of the 21st century has been very good to those of us interested in lichens. There were Brodo and the Sharnoffs' majestic Lichens of North America, the Hinds' The Macrolichens of New England (Memoirs of The New York Botanical Garden, Volume 96), the second edition of McCune and Geiser's Macrolichens of the Pacific Northwest: Second Edition, the completion of Nash, Gries, and Bungartz's three-volume Lichen Flora of the Greater Sonoran Desert Region, plus the new edition of the British Lichen Society's The Lichens of Great Britain and Ireland. (These last two are not available through Amazon.)
But these are all chiefly guidebooks to individual species, comprising mostly descriptions, keys, and photographs. To complement them, we now have the second edition of Lichen Biology, edited by Nash. This is a broad and detailed overview of what makes lichens tick, with chapters on anatomy and morphology, reproduction, biochemistry, ecology, physiology, biogeography, taxonomy, and more.
Lichen Biology won't help you tell an Usnea from a Bryoria but it will help you understand the many complex dimensions of these interesting symbiotic organisms. Others commenting on the first edition noted that it is a technical book. This is true, and some chapters are denser than others. (For someone like me who forgot everything he knew about organic chemistry many years ago, the chapter on secondary metabolites was especially challenging.)
My only reservation about Lichen Biology is that the pace of current research using DNA sequence data to establish phylogenies will make the chapters on systematics and taxonomy out of date very quickly.
I will give Lichen Biology four stars - terrific for serious students but destined to be a disappointment to a beginner. If you want a first book on lichens, this is not the place to start. Spring for the big one, Lichens of North America.