Over the past five years, Intelligent Automation Inc. (IAI) and its partners have been developing a unique, agentbased approach to online optimization that is intended for use in complex, large-scale systems operating in uncertain, dynamic environments. This approach involves a fundamental shift in paradigms, away from horizontally decomposed and logically distinct planning, scheduling and execution modules, towards communities of mediumgrained agents, in which each agent is responsible for a portion of the overall planning, scheduling and execution in the system. A major advantage of this shift towards vertically integrated intelligent agents is the increase in reactivity that can result from localizing the problems of planning, scheduling, and execution control. We also believe that this "bottom-up" philosophy has tremendous software engineering advantages when compared to centralized, top-down approaches to the construction of extremely large and complex systems. In addition, the ease with which such agent-based software systems can be distributed across networks of computers implies that large problems can be managed at relatively low cost.