Avian eggs possess very efficient and orchestrated systems to protect the embryo during incubation, until hatch. Although the internal components of the egg are assumed to be sterile, the surface of the eggshell is covered by microbes (essentially bacteria) that may contribute to prevent eggshell colonization by pathogenic bacteria, through direct inhibition and/or competitive exclusion. The composition of the eggshell microbiome is a heritage from both maternal microbiota (caeca/faeces) where the egg meets caecal secretions in the cloacal segment during oviposition, and from the nesting environment (contaminated litter/feathers and air environment including dust). At laying time, the egg surface is still moisturized, but will progressively dehydrate during incubation. The surface characteristics of the egg, the loss of the moisture layer and the presence of antimicrobial molecules composing the cuticle are likely to dictate the bacterial communities that will survive on the surface of the eggshell. Although the literature on the composition of the eggshell microbiome of eggs originating from current commercial chicken hens is quite sporadic, this talk aims to provide an overview of the bacterial communities that colonize the chicken eggshell surface, and will discuss the role of the eggshell microbiota as the first barrier against pathogenic bacteria.