Under a longstanding practice, a court sometimes treats as a request for habeas relief under 28 U. S. C. §2255 a motion that a pro se federal prisoner has labeled differently. Such recharacterization can have serious consequences for the prisoner, for it subjects any subsequent motion under §2255 to the restrictive conditions that federal law imposes upon a "second or successive" (but not upon a first) federal habeas motion. §2255, ¶ ;8. In light of these consequences, we hold that the court cannot so recharacterize a pro se litigant's motion as the litigant's first §2255 motion unless the court informs the litigant of its intent to recharacterize, warns the litigant that the recharacterization will subject subsequent §2255 motions to the law's "second or successive" restrictions, and provides the litigant with an opportunity to withdraw, or to amend, the filing. Where these things are not done, a recharacterized motion will not count as a §2255 motion for purposes of applying §2255's "second or successive" provision.