We have been using molecular and computational approaches to find regulatory RNAs, identify the messages that they regulate, and then investigate molecular consequences of these regulatory interactions as well as their functions during development, oncogenesis, and other biological processes.  This talk will describe our current understanding of microRNAs, the mechanisms by which they repress gene expression, a switch in the nature of translational control that occurs in early metazoan development, and how this switch influences the ultimate consequences of miRNA-mediated repression.