miRBase is a free online database of microRNA genes, developed and maintained by University of Manchester researchers. miRBase is the sole authority of what is and is not a microRNA, and therefore impacts all microRNA research worldwide, including in commercial and clinical sectors. The website attracts 20,000-30,000 monthly users, approximately 10% of whom are from commercial companies. miRBase data underpins commercially-successful research tools, diagnostics and therapeutics. More than 15 companies worldwide sell microRNA resources built from miRBase sequences. Novel therapeutics based on microRNAs defined by miRBase are in development and clinical trial. International genomic policy groups adopt miRBase standards on microRNAs.