Important aspects of plant development are under epigenetic control, that is, under the control of heritable changes in gene expression that are not associated with alterations in DNA sequence. It is becoming clear that RNA molecules play a key role in epigenetic gene regulation by providing sequence specificity for the targeting of developmentally important genes. RNA-based control of gene expression can be exerted posttranscriptionally by interfering with transcript stability or translation. Moreover, RNA molecules also appear to direct developmentally relevant gene regulation at the transcriptional level by modifying chromatin structure and/or DNA methylation.