piRNAs are a class of non-coding RNAs of approximately 26-32 nucleotides in length. The piRNA interacts with the PIWI (P-element-induced Wimpy Testis, subfamily of the Argonaute protein) to form a piRNA/PIWI complex, thereby silencing the transposable element to maintain genomic integrity, as well as phylogeny and spermatogenesis. The piRNA is produced by a primary transcript that traverses the entire piRNA cluster and is subsequently processed into mature piRNA. Although piRNA has been found in large numbers in many species, there are many unresolved problems in the field of piRNA that need further study.