Book excerpt: This book reviews the microbiology of the human gastrointestinal tract and how its composition and activities may affect host welfare. Drawing on the expertise of internationally recognised authors, a comprehensive account of gut microbiology is given. In particular, the nature of the microbiota, the fermentation process, gut flora modulation through diet (probiotics, prebiotics), molecular approaches for studying the bacteria, health outcomes associated with colonic microbial function and consumer aspects are all detailed. It is now believed that gut function, and colonic bacteria specifically, can play an important role in human nutrition and health. Whilst it has long been realised that the gastrointestinal microbiota can affect host well-being, the full extent of this interaction is only now emerging. This book gives a balanced review of current knowledge on how gut flora can be optimised for improved health and on some of the more important target outcomes. Its contents will therefore be of topical relevance to scientists and students involved in microbiology, gastroenterology, nutrition and the food industry.