All digital circuits have design margins for delay and power consumption. This thesis introduces an algorithm that exploits the design margin for delay to reduce power consumption instead, through the novel application of body bias to the transistors on the critical path. A runtime circuit monitors the activity of critical paths, and applies body bias to transistors on non-critical paths for specific input vectors where the value computed by the critical path is a don't care. In sub-100 nm CMOS devices, the application of adaptive body bias reduced leakage power while slightly increasing the signal propagation delay. When a portion of the circuit does not use up the whole clock cycle, the available slack can be used to reduce leakage power dissipation without compromising performance.