Over the last few years, the gut microbiota has been the focus of countless studies conducted both on mouse models and human population, aimed at analyzing its functions and interactions with the host, including nutrition, metabolic homeostasis, protection from infections and development of systemic and mucosal immunity both in inflammatory bowel disease (IBD) as well as other intestinal and extra-intestinal diseases. In IBD microbiota is impaired in overall composition and biodiversity, stability as well as functions. Microbial signature of IBD can be considered also a decrease in F. prausnitzii, increase of Proteonbacteria as well as the described increase of Candida albicans, Basidiomycota/Ascomycota ratio over Saccharomyces cerevisiae and of the Caudovirales over Microviridae. The indirect (through antibiotics, probiotics) and direct (through fecal microbiota transplantation) modulation of gut microbiota has relevant clinical implication in IBD management. In the near future role and clinical implication of gut microbiota characterization in the therapeutic personalized approach to IBD patients will eventually become clear.