This review discusses the emerging role of circular RNAs (circRNAs) in cancer, highlighting their potential as biomarkers and therapeutic targets. CircRNAs are stable, covalently closed RNA molecules that have gained attention due to their diverse cellular functions and conservation across species. They often exhibit tissue-specific expression patterns and can function as microRNA sponges, regulating gene expression. The review covers the current understanding of circRNA biogenesis, including back-splicing and lariat precursor mechanisms, and their regulation by RNA-binding proteins and miRNAs. It also explores the various functions of circRNAs, such as miRNA sponges, protein sponges, scaffolds, and roles in splicing and transcription. The review further discusses the involvement of circRNAs in the hallmarks of cancer, including proliferation, apoptosis, angiogenesis, and metastasis. It highlights the differential expression of circRNAs in various cancer types and tissues, emphasizing their potential as biomarkers. Finally, the review addresses the challenges and future directions in circRNA cancer research, including the need for standardized reporting, unbiased discovery methods, and the exploration of circRNA functions beyond miRNA sponging.This review discusses the emerging role of circular RNAs (circRNAs) in cancer, highlighting their potential as biomarkers and therapeutic targets. CircRNAs are stable, covalently closed RNA molecules that have gained attention due to their diverse cellular functions and conservation across species. They often exhibit tissue-specific expression patterns and can function as microRNA sponges, regulating gene expression. The review covers the current understanding of circRNA biogenesis, including back-splicing and lariat precursor mechanisms, and their regulation by RNA-binding proteins and miRNAs. It also explores the various functions of circRNAs, such as miRNA sponges, protein sponges, scaffolds, and roles in splicing and transcription. The review further discusses the involvement of circRNAs in the hallmarks of cancer, including proliferation, apoptosis, angiogenesis, and metastasis. It highlights the differential expression of circRNAs in various cancer types and tissues, emphasizing their potential as biomarkers. Finally, the review addresses the challenges and future directions in circRNA cancer research, including the need for standardized reporting, unbiased discovery methods, and the exploration of circRNA functions beyond miRNA sponging.