Despite advances in detection and therapies, breast cancer is still the leading cause of cancer death in women worldwide. The etiology of this neoplasm is complex, and both genetic and environmental factors contribute to the complicated scenario. Gene profiling studies have been extensively used over the past decades as a powerful tool in defining the signature of different cancers and in predicting outcome and response to therapies. More recently, a new class of small non-coding RNAs, microRNAs (miRNAs), able to regulate gene expression binding seed sequences on the 3'UTR of mRNA targets, has been linked to several human diseases, including cancer. An increasing amount of experimental evidence shows that miRNAs are aberrantly expressed in different tumour types, and that they can have a causal role in tumourigenesis. Here, we describe and discuss the evidence supporting the association between miRNAs and breast cancer, underlining their role in the development of this neoplasia, and the impact on putative innovative therapeutical approaches.