The engineering of biological systems requires a set of molecular tools that can be predictably applied to the design of sophisticated genetic systems. Recent advances in the held of RNA synthetic biology, particularly in the design of synthetic regulatory RNAs for the static and dynamic control of gene expression, have increased our ability to efficiently build various biological systems capable of performing programmed cellular behaviors. Furthermore, implementing these synthetic regulatory RNAs in biological systems highlights the potential for designing synthetic cell systems for chemical synthesis, environmental, agricultural, and medical applications. In this paper, we review current developments in synthetic regulatory RNAs for the static and dynamic control of gene expression and the potential applications of these tools. (C) 2013 Elsevier Ltd. All rights reserved.