Three-dimensional integration is an emerging fabrication technology that vertically stacks multiple integrated chips. The benefits include an increase in device density; much greater flexibility in routing signals, power, and clock; the ability to integrate disparate technologies; and the potential for new 3D circuit and microarchitecture organizations. This article provides a technical introduction to the technology and its impact on processor design. Although our discussions here primarily focus on high-performance processor design, most of the observations and conclusions apply to other microprocessor market segments.