The discipline that combines system elements which, working together, create unique structural and behavioral capabilities that none could produce alone. The degree to which well-designed systems-level architectures are critical to the success of large-scale projects—or the lack thereof to failure—has been dramatically demonstrated in recent years. The explosion of technological opportunities and customer demands has driven up the size, complexity, costs, and investment risks of such projects to levels feasible for only major companies and governments. Without sound systems architectures, these projects lack the firm foundation and robust structure on which to build. This conclusion holds whether the system is a satellite surveillance system, a crewed spacecraft, a stealth aircraft, a commercial airliner, a line of personal computers, or an advanced microprocessor.