In recent years mass media represented an important vehicle to develop the concept that everything we eat could have a positive or negative impact on our health; diet may modulate various physiological functions and may play destructive or beneficial roles in some diseases. On the other hand, numerous researchers support the concept that the maintenance of healthy gut microflora may provide protection against gastrointestinal disorders including infections and inflammatory bowel diseases. All of this information has increased the interest of consumers in their personal health and consequently toward healthy or organoleptic characteristic of foods. Consumers demand foods having a "medicinal value" and able to prevent illness and to modulate the intestinal microflora using live adjuncts micro-organisms called "probiotics". The selection of probiotics is based on some general microbiological criteria such us safety, health benefits, technological and digestive stress survival, intestinal cell adhesion and human origin. This book provides information on how this is done; discusses the efficacy of probiotics in preventing and treating microbial infections; the relation of probiotics and gastrointestinal diseases; enterococci; and the role of probiotics on immune mediated disorders.