Our understanding of the types and functions of RNA has increased dramatically over the last 50 years. Originally identified simply as coding or non-coding, RNA was recognized early as central to the process of transcribing and translating a gene into a protein. Over the last few decades, many new types of RNA have been discovered with specific functions, including snRNA, snoRNA, shRNA, miRNA, tmRNA, siRNA, saRNA, piRNA, and circRNA. These RNA molecules participate in a complex network that regulates how RNA is used in the cell and modifies gene expression. The multiple functions of RNA provide multiple pathways for exploiting RNA as a therapeutic molecule.