The essays that comprise this anthology of the best in ecology from Critical Reviews in Microbiology describe principles and practices in considerable detail. There is no attempt, however at a balanced presentation of the different groups of microorganisms or their activities. Likewise, some areas of current concern are considered cursorily and others not at all. Nevertheless, the book is an interesting and informative introduction to a growing endeavour. The combined experience and insight of the contributing authors will surely aid the reader to develop an ecological attitude, and to better appreciate microorganisms as determinants of environmental quality.