In this talk, we will give an overview of the BlueGene/L Supercomputer, being developed as part of a research partnership between IBM and the Lawrence Livermore National Laboratory. This massively parallel system of 65,536 nodes is based on a new architecture that exploits system-on-a-chip technology to deliver target peak processing power of 360 teraFLOPS (trillion floating-point operations per second). The machine is scheduled to be operational in the 2004-2005 time frame, at price/performance and power consumption/performance targets unobtainable with conventional architectures. We describe the challenges in designing a system software infrastructure that scales to 65,536 nodes, and how we have approached these challenges. We describe early experience with a small BlueGene/L prototype running in our laboratory.