The continued scaling of silicon technology beyond 0.25mm will provide the systems designer the possibility of creating complete systems on one integrated circuit At the same time this trend to miniaturization and lower operating voltages, permits an ever increasing degree of functional integration with the potential of dramatic improvements in performance, cost and power at the systems level. But, this drive to a single chip should be used to meet the goals of the system rather than to take advantage of the technology. This presentation will take on the system perspective of System On a Chip (SOC) to try to answer the questions of why should it be done, when should it be done and who should do it.