AbstractProteins produced by cap‐independent translation mediated by an internal ribosome entry site (IRES) in circular RNAs (circRNAs) play important roles in tumour progression. To date, numerous studies have been performed on circRNAs and the proteins they encode. In this review, we summarize the biogenesis of circRNAs and the mechanisms regulating circRNA‐encoded proteins expression. We also describe relevant research methods and their applications to biological processes such as tumour cell proliferation, metastasis, epithelial‐mesenchymal transition (EMT), apoptosis, autophagy and chemoresistance. This paper offers deeper insights into the roles that circRNA‐encoded proteins play in tumours. It also provides a theoretical basis for the use of circRNA‐encoded proteins as biomarkers of tumorigenesis and for the development of new targets for tumour therapy.