The transcriptome of a cell is represented by a myriad of different RNA 
molecules with and without protein-coding capacities. In recent years, advances 
in sequencing technologies have allowed researchers to more fully appreciate the 
complexity of whole transcriptomes, showing that the vast majority of the genome 
is transcribed, producing a diverse population of non-protein coding RNAs 
(ncRNAs). Thus, the biological significance of non-coding RNAs (ncRNAs) have 
been largely underestimated. Amongst these multiple classes of ncRNAs, the long 
non-coding RNAs (lncRNAs) are apparently the most numerous and functionally 
diverse. A small but growing number of lncRNAs have been experimentally studied, 
and a view is emerging that these are key regulators of epigenetic gene 
regulation in mammalian cells. LncRNAs have already been implicated in human 
diseases such as cancer and neurodegeneration, highlighting the importance of 
this emergent field. In this article, we review the catalogs of annotated 
lncRNAs and the latest advances in our understanding of lncRNAs.