The Monotrysia is a group of insects in the Lepidopteran order which is not currently considered to be a natural group or clade. The group contains only moths and most of these (apart from the recently discovered family Andesianidae) are small and are relatively understudied (compared to Ditrysia) in many regions of the world. The group is so named because the female has a single genital opening for mating and laying eggs, in contrast to the bulk of the Lepidoptera (Ditrysia), which have two female reproductive openings. They comprise all of the group Heteroneura but the Ditrysia.

The Monotrysia is a group of insects in the Lepidopteran order which is not currently considered to be a natural group or clade. The group contains only moths and most of these (apart from the recently discovered family Andesianidae) are small and are relatively understudied (compared to Ditrysia) in many regions of the world. The group is so named because the female has a single genital opening for mating and laying eggs, in contrast to the bulk of the Lepidoptera (Ditrysia), which have two female reproductive openings. They comprise all of the group Heteroneura but the Ditrysia.