MicroRNAs are small non-coding RNAs, transcribed from the genome, which have the capacity to regulate hundreds of other transcripts by base-pair binding of a 21 nucleotide sequence to a matching sequence on their target. We have demonstrated that microRNA-203 (miR-203) is strongly repressed by EMT. Re-expression of this microRNA in cells which have undergone EMT reverts them to an epithelial phenotpye, decreases their migratory capacity and prevents metastasis (Taube et al. 2013). We are working to characterize the downstream effectors regulated by miR-203 and the potential utility of elevating miR-203 expression in primary tumors.