The RNA world is bigger than we once thought. RNA interference is now regularly used by many labs to knock down specific genes, and we are only beginning to appreciate the variety of endogenous small RNAs and the processes they regulate. In Cell Science at a Glance (see p. 4689 + poster), Jean Finnegan and Marjori Matzke chart the known small RNA world. They survey the various forms of small RNA, the enzymes that generate them and the different consequences that pairing of a small RNA with its target sequence can have.