This study investigates the cell-type specific features of circular RNA expression. The authors developed an improved computational approach to identify circular RNA transcripts, which are prevalent in *Drosophila melanogaster* and estimated that circular RNA may account for about 1% of poly(A) RNA molecules in humans. Analysis of ENCODE consortium data revealed that the repertoire of genes expressing circular RNA, the ratio of circular to linear transcripts, and the pattern of splice isoforms are cell-type specific. The results suggest that the biogenesis of circular RNA is an integral, conserved, and regulated feature of gene expression programs. The study also found that circular RNA isoforms are resistant to RNase R treatment, indicating their specific identity. Additionally, the authors explored the regulation of circular RNA expression, noting that the abundance of circular RNA isoforms varies across cell types and genes, and that the use of specific splice donor and acceptor sites is regulated. The evolutionary conservation of circular RNA expression was also examined, showing that mouse orthologs of human genes with circular RNA products are more likely to encode circular RNAs. Overall, the findings highlight the significant role of circular RNA in gene expression and its potential regulatory functions.This study investigates the cell-type specific features of circular RNA expression. The authors developed an improved computational approach to identify circular RNA transcripts, which are prevalent in *Drosophila melanogaster* and estimated that circular RNA may account for about 1% of poly(A) RNA molecules in humans. Analysis of ENCODE consortium data revealed that the repertoire of genes expressing circular RNA, the ratio of circular to linear transcripts, and the pattern of splice isoforms are cell-type specific. The results suggest that the biogenesis of circular RNA is an integral, conserved, and regulated feature of gene expression programs. The study also found that circular RNA isoforms are resistant to RNase R treatment, indicating their specific identity. Additionally, the authors explored the regulation of circular RNA expression, noting that the abundance of circular RNA isoforms varies across cell types and genes, and that the use of specific splice donor and acceptor sites is regulated. The evolutionary conservation of circular RNA expression was also examined, showing that mouse orthologs of human genes with circular RNA products are more likely to encode circular RNAs. Overall, the findings highlight the significant role of circular RNA in gene expression and its potential regulatory functions.