In recent years there was a growing number of reports of new non-protein-coding RNAs which are implicated in the regulation of many cellular processes. They differ in many respects from already known housekeeping RNA species involved in protein biosynthesis (tRNA, rRNA) and RNA maturation or modification (RNase P RNA, snRNAs, snoRNAs). Regulatory RNAs (riboregulators) are expressed only in certain cell types, at particular stages of organism development or cell differentiation or in response to biotic and abiotic stimuli. Their expression is usually accompanied by the alteration of patterns of the expression of other genes. The mechanisms employed by riboregulators can affect transcription, pre-mRNA processing and translation. In the post-genomic era, the noncoding regulatory RNAs emerge as key determinants of organismal complexity, providing efficient and highly specific means for integration of various cellular processes.