Major advances in low-power design have enabled a broad spectrum of exciting new untethered applications. This paper will highlight some of the recent advances in the design of energy efficient systems. Emphasis will be placed on energy-agile fabrics—knobs that adapt system energy based on desired quality of service or signal statistics. For example, the use of an adaptive power supply voltages can minimize energy dissipation under varying system workload. The technology and circuit knobs required to control leakage power in low-voltage digital logic will also be described. Trends in portable systems, such as energy scavenging, will also be covered.