In recent years, advances in bioinformatics approaches have allowed a systematic characterization of circular RNAs (circRNAs) across a variety of cell types. Demonstration of cell type specificity, regulated expression, and conservation between species all suggest that circRNAs have functional importance. Especially, investigators have begun focusing on the possibility that circRNAs operate as part of competing endogenous RNA (ceRNA) regulatory networks that are proposed to play critical roles in normal development and in pathologic conditions like cancer.