Megaloptera is an order of insects. It contains the alderflies, dobsonflies and fishflies, and there are about 300 known species.

The Megaloptera were formerly considered part of a group then called Neuroptera, together with lacewings and snakeflies, but these are now generally considered to be separate orders, with Neuroptera referring to the lacewings and relatives (which were formerly called Planipennia). The former Neuroptera - particularly the lacewing group - are nonetheless very closely related to each other, and the new name for this group is Neuropterida. This is either placed at superorder rank, with the Endopterygota - of which they are part - becoming an unranked clade above it, or the Endopterygota are maintained as a superorder, with an unranked Neuropterida being a part of them. Within the endopterygotes, the closest living relatives of the neuropteridan clade are the beetles.