As silicon-based technologies mature in performance, yield and size, the design of highly integrated systems containing microprocessors, Memory, DSP, customized logic, and RF sections often on the same chip has become a real possibility. This level of integration of diverse computing elements is leading to a proliferation of microcomputer-based designs into computing and non-computing applications. These systems are increasingly being used in automotive, medical instrumentation, networking, process control, multimedia processing and consumer information appliances. The current effort in standardization of pre-designed IC blocks and interfaces is expected to accelerate this integration. This will make it possible for an IC designer to build complete systems on a single chip. Such System-on-Chip or SOC designs represent a special challenge in almost all aspects of IC/System design because of the requirements to integrate diverse components with little or no modifications to individual block or core cells. Tools and methodologies are needed for design and validation. In this talk, we present important issues in design tools for SOCs. The presentation touches upon four important aspects of SOC design technology: system modeling, system simulation and synthesis, mixed-signal design issues and software for SOCs.