Scrum is a set of project management practices aimed at coping with continual changes in requirements. It was introduced in the mid-'90s and claims many successes. Scrum is documented in the recent book by Ken Schwaber and Mike Beedle 5.
Scrum should be easy to adopt because it prescribes a few practices to manage the project but allows the maximum freedom about which programming practices to adopt. So it is suited to teams fervent about their practices and with a management asking for a proven track record of success. Scrum can also be easily merged with XP, as in the xP@Scrum approach, for instance.
[Editor's Note: For more information on Scrum and XP, read the article Scrum with XP by Ken Schwaber.]