Power and energy consumption have recently become key concerns for high-performance servers, especially when they are deployed in large cluster configurations as in data centers and Web hosting facilities. Research on power and energy management for these servers can ease installation, reduce costs, and protect the environment. Given these benefits, researchers have made important strides in conserving energy in these servers. Inspired by this initial progress, researchers are delving deeper into this topic. In this paper, we detail the motivation for this research, survey the previous work, describe a few ongoing efforts, and discuss the challenges that lie ahead.