This book is chiefly intended for those who are using microbicides for the protection of materials. Another purpose is to inform teachers and students working on biodeterioration and to show today's technical standards to those engaged in research and development activities in the microbicide field. When trying to classify or subclassify material-protecting microbicides according to their mode of action, such as membrane-active and electrophilic active ingredients, it became clear that a precise assignment was not always possible. For that reason, the author has resorted to chemistry's principle of classifying according to groups of substances, such as alcohols, aldehydes, ketones, acids, esters, and amides, thus providing the first necessary information about the microbicides' properties. The description of the various groups of substances includes, whenever possible, an outline of the mode and mechanism.