During the past few years, it has become clear that one type of ribonucleic acid (RNA) that does not code for protein plays central roles in epigenetic regulation. The emerging understanding is revolutionizing the way we think about the genome and how it is controlled. These RNAs are transcribed from the cell’s DNA and perform a wide variety of gene regulatory functions, some of which were once thought to be the exclusive purview of proteins. It has also become clear that a large part of the genome, previously thought to have no significant function, is highly actively expressed as non-coding RNA. Speakers in this symposium will describe recent studies of microRNAs that can target coding RNA for destruction, and of long non-coding RNAs that can deliver regulatory proteins to genes. Proper functioning of these RNAs is critical, as loss of their expression can have profound effects on development and cell growth.