MicroRNA.org is a comprehensive resource for microRNA target predictions and expression profiles. The target predictions are based on an improved version of the miRanda algorithm, which incorporates current biological knowledge and an up-to-date compendium of mammalian microRNAs. MicroRNA expression profiles are derived from a large-scale sequencing project of various mammalian tissues and cell lines. The resource provides a user-friendly graphical interface to explore potential target genes regulated by specific microRNAs, the cooperativity of multiple microRNAs on a single mRNA, and microRNA expression profiles in different tissues. The database structure and software architecture are designed to facilitate future updates and incorporate new discoveries. The resource is widely used by the research community to study microRNA regulation and expression, and future plans include expanding target predictions to additional organisms and integrating experimental data to enhance functional insights.MicroRNA.org is a comprehensive resource for microRNA target predictions and expression profiles. The target predictions are based on an improved version of the miRanda algorithm, which incorporates current biological knowledge and an up-to-date compendium of mammalian microRNAs. MicroRNA expression profiles are derived from a large-scale sequencing project of various mammalian tissues and cell lines. The resource provides a user-friendly graphical interface to explore potential target genes regulated by specific microRNAs, the cooperativity of multiple microRNAs on a single mRNA, and microRNA expression profiles in different tissues. The database structure and software architecture are designed to facilitate future updates and incorporate new discoveries. The resource is widely used by the research community to study microRNA regulation and expression, and future plans include expanding target predictions to additional organisms and integrating experimental data to enhance functional insights.