Small self-cleaving ribozymes are compact catalytic RNA motifs capable of mediating site-specific self-cleavage. Originally discovered in the minimal circular RNA genomes of plant viroids and viral satellites, they were long considered rare biological curiosities limited to these unusual infectious RNAs. However, subsequent discoveries revealed that these small ribozymes are widespread across all domains of life, including eukaryotic genomes, where they are often embedded within retrotransposons or even within host genes. Their structural diversity reflects a multitude of evolutionary origins and functional adaptations, ranging from genome processing during rolling-circle replication to potential regulatory roles in mRNA maturation, stability, and gene expression in mammals and other vertebrates. Notably, the discovery of retrozymes, a family of non-autonomous retrotransposons with embedded ribozymes that generate abundant circular RNAs, highlights a conserved and efficient natural pathway for circRNA biogenesis in both plants and animals. These findings collectively underscore that small self-cleaving ribozymes are not only ancient and pervasive but also highly adaptable, influencing genome evolution, the mobility of genetic elements, and the regulation of gene expression. As genomic technologies continue to advance, it is likely that additional classes and functions of small ribozymes will be uncovered, further illuminating the fundamental roles of RNA catalysis in biology.