Bifidobacteria are high G+C Gram positive bacteria belonging to the phylum Actinobacteria. In recent years bifidobacteria have attracted a lot of attention because of their perceived positive contribution to the functionality of the human gastro intestinal tract. For this reason, scientific research on these bacteria has been rapidly expanding, in particular in areas such as genomics, molecular ecology and genetics. Ecological studies together with genome-based sequencing efforts have provided scientific evidence for the considerable contribution of bifidobacteria to the human gut microbiome. Furthermore, bifidobacterial genomics has revealed various genetic adaptations of these bacteria to the gastrointestinal niche.