This document summarizes dynamic energy management techniques in cloud data centers. It discusses that cloud data centers consume enormous amounts of energy, resulting in high costs and environmental impacts. It then categorizes energy management approaches as either static or dynamic. Dynamic energy management techniques dynamically reconfigure hardware and software systems based on workload variability to optimize energy usage. The document surveys techniques at the hardware level including for processors, networks, and storage, and also virtualization-assisted techniques like server consolidation and virtual machine placement and migration. The goal of these dynamic techniques is to improve energy efficiency in cloud data centers through runtime adaptation.