The field of RNA has undergone a revival in recent years with the discovery of RNA interference and related gene regulatory mechanisms, as well as the uncovering of new RNA species. It is impossible to cover the vast field of RNA in a single issue, so we've tried to highlight some particularly fast-moving areas and innovative approaches to studying RNA.

The first microRNA (miRNA) was reported just over a decade ago. On page 376, V. Narry Kim outlines our current understanding of the multistep process of miRNA biogenesis, which comprises transcription and the subsequent processing and maturation of miRNAs. Also, recent progress in elucidating the mechanisms by which mRNAs are localized intracellularly is reviewed by Daniel St Johnston on page 363. In particular, new in vivo imaging technologies have begun to reveal the mechanisms by which motor proteins transport mRNAs in cells.

Like most RNA processes, alternative splicing is traditionally studied in simple systems that comprise a single gene. But, as discussed by Christopher W. J. Smith and colleagues on page 386, traditional approaches are now being complemented by genome-wide approaches for identifying new regulatory elements and factors. Self-splicing and other catalytic RNAs are the subject of the Review by Martha J. Fedor and James R. Williamson (page 399). RNA catalysis is turning out to be far more fascinating than was initially thought, because RNA enzymes seem to be as diverse as proteins in their repertoire of catalytic strategies.

You'll find this, and more, in this month's issue. Please visit the accompanying Web Focus (www.nature.com/nrm/focus/rna), which contains a selection of the top RNA papers published recently by the Nature Publishing Group.