The vaginal microbiota and the immunologic milieu that derives are a dynamic and complex ensemble. A normal vaginal microbiota is mainly constituted by Lactobacillus sp.. This bacterium, thanks to the production of metabolites (lactic acid, hydrogen peroxide, bacteriocin) and stimulating the immune system toward an anti-inflammatory switch, can maintain the stability of vaginal microbiota and inhibit pathogen bacteria proliferation. Multiple factors affect vaginal microbiota composition. They can lead to high diversity and rise of anaerobic bacteria that enhance chronic inflammation, vaginal epithelial barrier damage, risk of STI transmission, infertility, preterm labor, PID. Research about this issue has intensified in the last decade, due to the development of molecular biology techniques that allow to isolate specific species of bacteria and analyse their specific functions. However, the understanding of the mechanisms through which the shifts in the microbiota can affect the health state and the immune system of the individual is still far. This constitutes a frontier for the development of prevention, diagnosis and therapeutic strategies.