X.S.E.

X.S.E. refers to a comic book series and two mutant organisations within the Marvel Universe

* Xavier's Security Enforcers, the militia created to police the mutant population in Bishop's future, and which he and his sister Shard were members of, and the series of the same name (usually abbreviated "XSE").
* X-Treme Sanctions Executive, a United Nations-backed organisation led by Storm in the present day.