In this paper, methods to achieve low-power and high-speed VLSI's are described with the emphasis on cooperation between levels. To suppress the leakage current in a standby mode, Boosted Gate MOS (BGMOS) is effective, which is based on cooperation between technology level and circuit level. To reduce the power in an active mode, VDD-hopping and VTH-hopping are promising, which are cooperative approaches between circuit and software. The power consumed in an interconnect system is another issue in low-voltage deep-submicron designs. A cooperative approach between VLSI and assembly to the interconnect power problem is also discussed.