The human gut microbiota is the set of all organisms living in the human gastrointestinal tract. This amazingly diverse community is composed of the 3 domains of life and their respective viruses. Since the emergence of molecular techniques for the study of microbial communities, the gut microbiota has been a major target of study and large consortia such as the HMP in the USA and MetaHIT in Europe have devoted a great deal of resources to characterize these communities. However, the major effort to study these communities has been made on their prokaryotic component ignoring for the most part the viral component. In fact, this component may be greater in number and diversity than the bacterial component itself. Viruses are present in any environment where a potential host is found and their predation dynamics, lytic or lysogenic cycles can have important consequences on the dynamics and behavior of the community in general. The study and characterization of the relationships between viruses (with bacterial or eukaryotic hosts) and their diverse implications in the community and therefore their consequences in the health of the human host, are an important objective of the group’s research.