Agility without discipline cannot scale, and discipline without agility cannot compete. Agile methods are now mainstream. Software enterprises are adopting these practices in broad, comprehensive delivery contexts. There have been many successes, and there have been disappointments. IBM's framework for achieving agility at scale is based on hundreds of successful deployments and dozens of disappointing experiences in accelerating software delivery cycles within large-scale organizations. Our collective know-how points to three key principles to deliver measured improvements in agility with high confidence: Steer using economic governance, measure incremental improvements honestly, and empower teams with disciplined agile delivery. This paper elaborates these three principles and presents practical recommendations for achieving improved agility in large-scale software delivery enterprises.