This white paper-- along with its companion white paper, "Greening the data center with IBM Tivoli software: an integrated approach to managing energy"-- discusses the importance of managing energy consumption in data centers and how systems management technologies contribute to green management. The paper provides an overview of green data centers and the significant role played by direct and indirect power consumption in today's data centers, as well as technology aspects of green data center management. It then describes the specific ways IBM Tivoli solutions can help optimize energy use in the data center.