The International Committee on Microbial Ecology (ICOME) sponsors both the Interna­ tional Symposium on Microbial Ecology, held in various parts of the world at three-year intervals, and the publication of Advances in Microbial Ecology. Advances was estab­ lished to provide a vehicle for in-depth, critical, and even provocative reviews in microbial ecology and is now recognized as a major source of information for both practicing and prospective microbial ecologists. The Editorial Board of Advances nor­ mally solicits contributions from established workers in particular areas of microbial ecology, but individuals are encouraged to submit outlines of unsolicited contributions to any member of the Editorial Board for consideration for pUblication in Advances. Chapters in Volume 11 of Advances in Microbial Ecology include those on micro­ bial transformations of chitin by G. W. Gooday, organic sulfur compounds by D. P. Kelly and N. A. Smith, and phosphorus, including its removal in waste water treatment plants, by D. F. Toerien, A. Gerber, L. H. Lotter, and T. E. Cloete. The importance of diffusion processes in microbial ecology is discussed by A. L. Koch, and 1. I. Prosser reviews the application of mathematical modeling to nitrification processes. Considera­ tions of particular ecosystems include the Antarctic by D. D. Wynn-Williams and Australian coastal microbial mats by G. W. Skyring and 1. Bauld. Other chapters include the regulation of N2 fixation by H. W.