This presentation shows how to apply a whole-system approach to the energy use in data centers in order to provide 95–99% energy savings. The authors present strategies for saving energy that have been applied effectively to new and existing data centers. For example, using a centralized cooling system can cut energy use by half. New data centers can be designed for significant energy savings. Existing data centers also offer the potential to be retrofitted for optimal virtualization, efficient hardware, airflow management, and lighting. The presentation shows that these changes to existing building can reduce energy use and costs. Best practices by data centers can reduce power consumption dramatically, thereby reducing environmental and business risks.