The miRBase database provides integrated interfaces for microRNA (miRNA) sequence data, annotation, and predicted gene targets. It serves three main functions: the miRBase Registry assigns names to miRNAs before publication, the miRBase Sequences database is the primary repository for miRNA sequence data and annotation, and the miRBase Targets database contains predicted miRNA target genes. The database is available at http://microrna.sanger.ac.uk/. miRNAs are non-coding RNA molecules that regulate gene expression by binding to complementary regions of messenger RNA. They are involved in various biological processes, including development, cell death, and disease. The biogenesis of miRNAs involves processing from a precursor sequence, and they are transcribed by RNA polymerase II. The miRBase Registry ensures consistent gene naming, assigning names based on guidelines agreed by researchers. miRNA names are assigned after a manuscript is accepted for publication. miRNAs are given sequential numerical identifiers, with species-specific prefixes. The database uses stable accessions to track sequence entities. The miRBase Sequences database contains sequences of all published mature miRNA sequences, along with their predicted source hairpin precursors and annotations. It has grown significantly in the past two years, from 506 entries to 2909 entries in 36 species. The database provides genomic coordinates and links to Ensembl for genomic context. The miRBase Targets database includes information about miRNA genomic targets. It uses a pipeline to predict miRNA targets based on computational methods. The database provides high-quality target predictions and allows users to compare third-party predictions. The miRBase database is freely available for online searching and downloading sequences and annotations.The miRBase database provides integrated interfaces for microRNA (miRNA) sequence data, annotation, and predicted gene targets. It serves three main functions: the miRBase Registry assigns names to miRNAs before publication, the miRBase Sequences database is the primary repository for miRNA sequence data and annotation, and the miRBase Targets database contains predicted miRNA target genes. The database is available at http://microrna.sanger.ac.uk/. miRNAs are non-coding RNA molecules that regulate gene expression by binding to complementary regions of messenger RNA. They are involved in various biological processes, including development, cell death, and disease. The biogenesis of miRNAs involves processing from a precursor sequence, and they are transcribed by RNA polymerase II. The miRBase Registry ensures consistent gene naming, assigning names based on guidelines agreed by researchers. miRNA names are assigned after a manuscript is accepted for publication. miRNAs are given sequential numerical identifiers, with species-specific prefixes. The database uses stable accessions to track sequence entities. The miRBase Sequences database contains sequences of all published mature miRNA sequences, along with their predicted source hairpin precursors and annotations. It has grown significantly in the past two years, from 506 entries to 2909 entries in 36 species. The database provides genomic coordinates and links to Ensembl for genomic context. The miRBase Targets database includes information about miRNA genomic targets. It uses a pipeline to predict miRNA targets based on computational methods. The database provides high-quality target predictions and allows users to compare third-party predictions. The miRBase database is freely available for online searching and downloading sequences and annotations.