Long non-coding RNAs (lnc)RNAs have emerged as a new paradigm in epigenetic regulation of the genome. Thousands of lncRNAs have been identified and observed in a wide range of organisms. Unlike mRNA, lncRNA have no protein-coding capacity. So, while their function is not entirely clear, they may serve as key organizers of protein complexes that allow for higher order regulatory events. Discovering these functions has been the result of intense research done of the last few years, and lncRNA research has had several critical developments during that time. This book consolidates these ideas and models to better examine the most important issues in lncRNA biology. This includes critical studies that have led to the discovery and annotation of lncRNAs in numerous species, and the molecular mechanisms for a few lncRNA that have begun to emerge.