The human gastrointestinal tract represents an environment which is a densely populated home for a microbiota
that has evolved to positively contribute to host health. At birth the essentially sterile gastrointestinal tract (GIT) is
rapidly colonized by microorganisms that originate from the mother and the surrounding environment. Within a
short timeframe a microbiota establishes within the (breastfed) infant’s GIT where bifidobacteria are among the
dominant members, although their numerical dominance disappears following weaning. The numerous health
benefits associated with bifidobacteria, and the consequent commercial relevance resulting from their
incorporation into functional foods, has led to intensified research aimed at the molecular understanding of
claimed probiotic attributes of this genus. In this review we provide the current status on the diversity and ecology
of bifidobacteria. In addition, we will discuss the molecular mechanisms that allow this intriguing group of bacteria
to colonize and persist in the GIT, so as to facilitate interaction with its host.