Circular RNAs (circRNAs), formed by nonsequential back-splicing of pre-messenger RNA (pre-mRNA) transcripts, have been widely concerned in recent years. With advances in high-throughput RNA sequencing (RNA-seq) technology, previous work has revealed that a large number of circRNAs, which are endogenous, abundant and stable in mammalian cells, may be involved in atherosclerotic vascular disease risk, neurological disorders, prion diseases and carcinomas. Remarkably, interaction between circRNAs and microRNA has already been observed to perform a significant role in a variety of cancers, including gastric cancer and colorectal cancer. Recent work has suggested that circRNAs may play critical roles in the initiation and development of cancers and could become potential new biomarkers for cancers. Herein, we review the current understanding of the roles of circRNAs in cancers and the potential implications of circRNAs in cancer-targeted therapy.