Breastfeeding is a major determinant of human health. Breast milk is not sterile and ecological large-scale sequencing methods have revealed an unsuspected microbial diversity that plays an important role. However, microbiological analysis at the species level has been neglected while it is a prerequisite before understanding which microbe is associated with symbiosis or dysbiosis, and health or disease. We review the currently known bacterial repertoire from the human breast and milk microbiota using a semiauto-mated strategy. Total 242 articles from 38 countries, 11,124 women and 15,489 samples were included. Total 820 species were identified mainly composed of Proteobacteria and Firmicutes. We report variations according to the analytical method (culture or molecular method), the anatomical site (breast, colostrum or milk) and the infectious status (healthy control, mastitis, breast abscess, neonatal infection). In addition , we compared it with the other human repertoires. Finally, we discuss its putative origin and role in health and disease. Breastfeeding has been associated with the health of the child and the mother, regardless of geography and socioeconomic level [1], child's growth and cognitive development [1,2]. Human studies suggest a protective effect against diarrhea, necrotizing enterocolitis, otitis media and respiratory infections in the short term and against leukemia, malocclusion, inflammatory bowel disease, malnutrition including kwashiorkor, obesity and diabetes in the long term [1,3,4]. Up to half of deaths caused by infections in children aged 6-23 months may be associated with the absence of adequate breastfeeding [1]. Breastfeeding has also been associated with a protective effect for mothers against breast cancer and possibly against ovarian cancer and diabetes [1]. In addition to nutrients, bioactive molecules such as human milk oligosaccharides, human maternal cells but also extracellular vesicles [5-8], milk contains many microbes and is therefore not sterile. The importance of the microbial diversity of human milk for the health of the offspring has been largely neglected to date. More recently, an increasing number of studies have reported an unsuspected diversity, including many health-promoting bacteria (probiotics) in the breast, colostrum or milk [9-11] but also bacteria usually considered pathogenic and frequently found in healthy controls [12]. The milk microbiota likely plays a critical role in the colonization of the child's digestive tract and in the development of its immunity [13-16]. Prolonged exclusive breastfeeding is associated with reduced diarrhea-related gut microbiota dysbiosis and microbiota differences that persist for life [8]. The disruption of this ecosystem has also been associated with maternal diseases, such as lactational mastitis and breast cancer [17-20]. Breast bacteria could also play a role in maintaining healthy breast tissue, including stimulating host immunity [17]. Many questions remain unanswered regarding the microbiome, such as the fact that microbes considered pathogenic are frequently found in controls, the mechanism by which the microbiota impacts immune development and how dysbiosis leads to gut inflammation [8]. Researchers suggested that future studies should employ metagenomics, metatranscriptomics and metabolomics approaches to understand the complete taxonomical, func