The subject of the book is the analysis of microbiological features of the genus bifidobacteria and their use as probiotics. Main topic of interest is the critical evaluation of bifidobacteria as probiotics, in particular regarding the capacity to 'colonize' the gastrointestinal tract, their safety of use, the therapeutical and nutritional effects and their capacity to stimulate the immunological system. All pictures of all species are reported, some scanning electron microscopy pictures show bifidobacteria directly on human mucosa.