Genome integrity of germline is essential for the survival of any species. A dedicated defence mechanism based on small RNA called piRNA (PIWI-interacting RNA) has evolved to protect the germline from the deleterious effects of transposon mobility in genomes such as mutations, deletions or chromosomal rearrangements. The piRNA machinery ensures genomic integrity to germ cells by setting a response similar to the immune system. The recognition of the threat is mediated by sequence complementarity between a vast repertoire of piRNAs and the intruders, and initiates a rapid and efficient degradation of the targets. Akin to acquired immunity, the response is memorized throughout generations thanks to epigenetic modifications. Investigations are progressing to unravel the mysterious mechanisms of this exciting class of non coding RNAs. This review summarizes some of the recent advances on this exceptional immunity that protects transmission of genetic information.