PURPOSE OF REVIEW: Studies have illustrated that the healthy human microbiome (i.e. the communities of microbes, their genomic content and interaction with the host) plays a role in the maintenance of immune homeostasis. Perturbation of these communities is an emerging characteristic of an increasing number of inflammatory diseases. The goal of this article is to review the current literature on both respiratory and gut microbiomes and their established relationship with allergy and asthma. RECENT FINDINGS: Multiple studies have demonstrated airway microbiota dysbiosis, characterized by Proteobacteria expansion in the lower airways, to be a consistent trait of established adult asthma. Members of this phylum are associated with disease features such as bronchial hyperreactivity or corticosteroid resistance. Emerging evidence implicates the neonatal gut microbiome as playing a significant role in the development of childhood atopy, a common precursor to asthma. Murine studies have demonstrated that specific bacterial species (e.g. Lactobacillus johnsonii, Bacteroides fragilis) and microbial metabolites (e.g. the short-chain fatty acid propionate), when supplemented to animals, confer protection against allergen-induced airway disorders. SUMMARY: The emerging view of atopy and asthma is one consistently related to inappropriate microbial community composition and function in both the airway and gastrointestinal tract. This opens up the possibility that strategies to rationally manipulate microbiota at these sites may represent a novel approach to disease prevention or management.