Non coding RNAs (ncRNAs) consist of a large portion of poly-A tailed mature RNAs. They are single stranded molecules, which are involved in the regulation of gene expression at the post-transcriptional level in a cell. There are two types of ncRNAs, which are regulatory ncRNAs and infrastructural ncRNAs. Small interfering RNAs (siRNAs), microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and piwi-interacting RNAs (piRNAs) are the four types of regulatory ncRNAs. The expression of thousands of genes is regulated through ncRNAs and this regulation can take place in either cis or trans. NcRNAs must be integrated into regulatory networks for the identification of molecular driver events. The two largest members of the ncRNA family, which includes long non coding RNA (lncRNA) and micro RNA (miRNA), play significant regulatory roles in gene expression. They are also involved in a variety of physiological processes including programmed cell death. This book unravels the recent studies on non coding RNA biology. It attempts to understand the regulation of non coding RNAs. For all those who are interested in ncRNAs, it can prove to be an essential guide.