AbstractShort interspersed elements (SINEs) are mobile genetic elements that invade the genomes of many eukaryotes. Since their discovery about 30 years ago, many gaps in our understanding of the biology and function of SINEs have been filled. This review summarizes the past and recent advances in the studies of SINEs. The structure and origin of SINEs as well as the processes involved in their amplification, transcription, RNA processing, reverse transcription, and integration of a SINE copy into the genome are considered. Then we focus on the significance of SINEs for the host genomes. While these genomic parasites can be deleterious to the cell, the long‐term being in the genome has made SINEs a valuable source of genetic variation providing regulatory elements for gene expression, alternative splice sites, polyadenylation signals, and even functional RNA genes. WIREs RNA 2011 2 772–786 DOI: 10.1002/wrna.91This article is categorized under: RNA Processing > Processing of Small RNAs RNA in Disease and Development > RNA in Development