Chironex is a genus of box jellyfish in the Chirodropidae family. Traditionally, only a single species, C. fleckeri, was recognized in this genus, but in 2009 a second species, C. yamaguchii, was described. Their stings are highly venomous, and both species have caused human fatalities. Based on present knowledge, the genus is restricted to the central Indo-Pacific, ranging from to southern Japan to northern Australia.