Book excerpt: The complexity of the microbial population of the animal gastro-intestinal trac has been recognised long ago. However, thus far, investigations have been limited to a few major groups, considered to be dominating, and pathogens that are detrimental and may case diseases and concomitant financial losses in the production animal. Thanks to the latest developments, including improved micriological detection and sampling techniques, and the application of molecular tools to monitor the presence of specific strains in the intestine, our knowlede has increased rapidly in recent years. In addition, new approaches towards improving and/or stabilising animal health, are addressed, with special emphasis on probiotics, and also with regard to the use selected bacterial strains as vehicles for delivery of pharmaceutically active compounds to the muscosa. The book is unique in several respects, not only by its coverage of an extremely wide area in animal gut microbiology, but also by the fact that production animals such as fish and reindeer are included. Scope and treatment of the subject matter and the kind of information that can be found in the volume: Colonisation and development (succession), and mucosal surface composition of the normal microbial population flora in the healthy animal are addressed, whilst estensive information is given on diverse and dominating bacterial populations of different animal types. Reference is also made to those microbial groups considered to be of special benefit to the health and immune protection of the (young) animal bacteria. The development and application of models of the Gastro-Intestinal tract provides a solid basis for studying gut microbial interactions, whilst molecular approaches and the us of molecular tools to monitor the presence of specific strains in the intestine is treated in a comprehensive manner. Wide coverage of different animal types and their gut microbial ecology Extensive and partly new information on the major microbial groups associated with the animal gastro-intestinal tract The book is unique and partly new information and up-to-date information proved in the chapters as a whole