SINEs (short interspersed elements) are mobile elements of approximately 100～500 bp that are often present as more than 10⁵ copies per genome. They can be divided into families and subfamilies according to the mutational or diagnostic sequence loci. SINEs are widespread in eukaryotic genomes and create additional sequence combinations through dispersal and exchange of genetic information. So, they are believed to be of major importance in creating genetic diversity, gene inactivity, new gene, and especially in gene expression and gene regulation. Almost all SINEs reported to date are derived from tRNAs, with the exception of the primate Alu and the rodent B1 families, which are derived from 7SL RNA. The tRNA-derived SINEs have a composite structure, with a region homologous to a tRNA, a middle tRNA-unrelated region, and a terminal AT-rich region. Each SINE contains an internal promoter for RNA polymerase Ⅲ and lacks open reading frames. “Master source gene model”, “multiple source gene model”, “transposon model (parasitism model)”, and “horizontal transfer model”have been postulated to explain the origin and evolution of SINEs. The observation of their molecular phylogeny was made with examples of salmons, whales and artiodactyls，hominoid primates，and western Palearctic water frogs. Their application to genetic profiles and antitumor technique was also introduced.