Increasing microprocessor performance has historically been accompanied by increasing power and increasing on-chip power density, both of which present a cooling challenge. In this paper, the historical evolution of power is traced and the impact of power and power density on thermal solution designs is summarized. Industrial and academic researchers have correspondingly increased their focus on elucidating the problem and developing innovative solutions in devices, circuits, architectures, packaging and system level heatsinking. Examples of some of the current packaging and system thermal solutions are provided to illustrate the strategies used in their design. This is followed by a brief discussion of some of the future trends in demand and solution strategies that are being developed by academic and industrial researchers to meet these demands. Potential opportunities and limitations with these strategies are reviewed.