This study investigates the abundance, conservation, and functional implications of circular RNAs (circRNAs) in human fibroblasts. The authors developed a method called CircleSeq to identify circRNAs by enriching linear RNAs with an RNA exonuclease, RNase R, followed by high-throughput sequencing. They identified over 25,000 distinct circRNAs in human fibroblasts, which were more stable than their linear counterparts and often more abundant. These circRNAs were found to be derived from 14.4% of actively transcribed genes. The study also found that paralogous kinases *HIPK2* and *HIPK3* produced abundant circRNAs from their second exons in both humans and mice. Bioinformatic analysis revealed that circRNAs often contain long introns with complementary ALU repeats, suggesting a role in gene expression regulation. Additionally, the authors showed that circRNAs can be targeted by siRNAs and are highly stable, preferentially localized in the cytoplasm. The findings suggest that circRNAs are not random products of splicing but may play important roles in gene regulation.This study investigates the abundance, conservation, and functional implications of circular RNAs (circRNAs) in human fibroblasts. The authors developed a method called CircleSeq to identify circRNAs by enriching linear RNAs with an RNA exonuclease, RNase R, followed by high-throughput sequencing. They identified over 25,000 distinct circRNAs in human fibroblasts, which were more stable than their linear counterparts and often more abundant. These circRNAs were found to be derived from 14.4% of actively transcribed genes. The study also found that paralogous kinases *HIPK2* and *HIPK3* produced abundant circRNAs from their second exons in both humans and mice. Bioinformatic analysis revealed that circRNAs often contain long introns with complementary ALU repeats, suggesting a role in gene expression regulation. Additionally, the authors showed that circRNAs can be targeted by siRNAs and are highly stable, preferentially localized in the cytoplasm. The findings suggest that circRNAs are not random products of splicing but may play important roles in gene regulation.