The literature in microbial ecology is growing rapidly. Journals in many countries dealing with microbiology, ecology, environmental sciences, and environmental technology are publishing an ever-increasing number of papers, and these reports are providing microbial ecologists with a wealth of information. This body of data is now so large and the research is published in so many journals and mono­ graphs that maintaining an overview of the development of the field grows more difficult. The role of Advances in Microbial Ecology thus becomes more obvious with time. The articles in the present volume encompass an array of topics appropriate to the development of the discipline of microbial ecology. Both terrestrial and aquatic ecosystems are subjects of attention, and a variety of microbiological groups come under review. Furthermore, methodological problems and ap­ proaches are not overlooked. The ecology of protozoa, constraints on their populations, and their role in nutrient cycling and energy flow are considered by J. D. Stout. A unique micro­ environment is discussed by B. Norkrans, the surface microlayer of aquatic eco­ systems, and Dr. Norkrans presents information on a field that has blossomed in the last few years. The subject of the review by H. S. Lowendorf is the genus Rhizobium, a group of bacteria whose importance has grown as the cost of fuel for production of nitrogen fertilizers and ultimately for protein production has increased.