Reducing the energy consumed in the use of computing devices is becoming a major design challenge. While the problem obviously must be addressed with improved low-level technology, we claim there is potential value in a higher-level perspective, as well. In our approach, the needs of applications serve as the driving force for the development of power-management functions in the operating system and of a power-based API that allows a partnership between applications and the system in setting energy policy. The development of a PalmPilot application is used as an illustration. We advocate that reducing energy consumption should be raised to first-class status among performance goals when software is being designed. In support of this objective, new programming models, measurement tools, and system support mechanisms must be developed. These needs motivate our Milly Watt Project.