A large fraction of mammalian genome can be transcribed to produce various RNAs, of which only a small subset can serve as the template for protein translation. The RNAs that do not code for proteins are collectively referred as non-coding RNA, which can serve as key functional components or regulatory molecules of gene expression. The best understood regulatory non-coding RNAs include microRNAs (miRNAs) that control degradation and/or translation of mRNAs and long non-coding RNAs (IncRNAs) that often control chromatin structure and gene transcription. Depending on the specific targets regulated by non-coding RNAs, the biological roles of the regulatory non-coding RNA can be very diverse. In the past decade, novel functions of many non-coding RNAs have been discovered that control important biological pro-cesses such as cell differentiation; however, current work may only present a tip of iceberg of all possible functions of non-coding RNAs. In this issue, one review and four research papers provide new insights into the biological roles of regulatory non-coding RNA.