Selected potential mechanistic pathways that could underlie the association between RSV infection in infancy and childhood asthma. The results of recent studies suggest that RSV infection in infancy could lead to childhood asthma though alterations in the human microbiome, airway epithelial cell development, airway hyperresponsiveness, and immune development. Host genetics, viral genetics, and gene-by-virus interactions, among others, can also impact this association. Definition of abbreviation: RSV = respiratory syncytial virus.