MicroRNAs (miRNAs) are a family of endogenous, small, noncoding RNA molecules that modulate physiological and pathological processes by post-transcriptional inhibition of gene expression. They were first recognised as regulators of development in worms and fruitflies. In recent years extensive research has explored their pivotal role in the pathogenesis of human diseases. Over 1,000 human miRNAs have been discovered to date; however, the biological function and protein targets for the majority remain to be uncovered. Within the respiratory system, miRNAs are important in normal pulmonary development and maintaining lung homeostasis. Recent studies have also begun to reveal that altered miRNA expression profiles may be associated with pathological processes within the lung and lead to the development of various pulmonary diseases, ranging from inflammatory diseases to lung cancers. Advancing our understanding of the role of miRNAs in the respiratory system will help provide new perspectives on disease mechanisms and reveal intriguing therapeutic targets and diagnostic markers for respiratory disorders.