Energy is an important resource for a wide range of computer systems from laptops to data centers and clouds. There has been considerable recent research on the topic of of improving energy efficiency, cutting across different areas of Computer Science including Computer Architecture (e.g., energy efficient processor design), Networking (e.g., putting the network to sleep), Storage (e.g., exploiting idle I/O periods to spin down disks), Distributed Systems (e.g., capacity provisioning), Mobile Systems (e.g., putting the radio receiver to sleep in a smartphone), and Modeling/Analytics (e.g., modeling a server's power consumption). This course covers the recent research trends in energy-efficient computing, focusing specifically on themes and techniques for achieving efficiency in computer systems.