usage of the terms substrate and substratum. A substrate (pI.: substrates) is a material utilized by microorganisms, generally as a source of energy. A substratum (pI.: substrata) is asolid surface to which a microorganism mayattach. REFERENCES (1) Marshall, K.C. 1976. Interfaces in Microbial Ecology. Cambridge, MA: Harvard University Press. (2) ZoBell, C.E. 1943. The effect of solid surfaces upon bacterial activity. J. Bacteriol. 46: 39-56. Standing, left to right: Paul Rutter, Rolf Freter, Mike Silverman, lan Robb, Hinrich Mrozek, Frank Dazzo, David Gingell Seated, left to right: Garth Jones, Stanislawa Tylewska, Staffan Kjelleberg, Ellen Rades-Rohkohl, Kevin Marshall Microbial Adhesion and Aggregation, ed. K.C. Marshall, pp. 5-19. Dahlem Konferenzen 1984. Berlin, Heidelberg, New York, Tokyo: Springer-Verlag. Mechanisms of Adhesion Group Report P.R. Rutter, Rapporteur F.B. Dazzo H. Mrozek R. Freter E. Rades-Rohkohl D. GingeIl I.D. Robb G.W. Jones M. Silverman 8. Kjelleberg 8. Tylewska K.C. Marshall INTRODUCTION The subject, Mechanisms of Microbial Attachment, has proved to be a fertile sour ce of argument between both microbiologists and physical chemists. In order to find common ground for discussion, the group endeavored to come to a consensus regarding a number of definitions pertinent to the subject. Some of these are described in the text and others will be found at the end of this report.