The complexity of many large-scale systems in the aerospace, automotive, business, civic, and manufacturing fields is outpacing our ability to effectively simulate, design, and optimize such systems.Complex national and international engineering projects are increasingly well over budget and behind schedule.While there may be a number of contributing factors, the enormous complexity of the designed systems certainly plays a role.I surmise that designing and optimizing such systems without an understanding of some of the elegant principles of complex systems may lead to disastrous consequences.Many of these principles are emerging in the design research community, allowing for innovative approaches for the predictive simulation and advanced optimization of large-scale systems.As a result, I present a number of these principles in an effort to highlight the emerging research in the science of designing complex systems, illuminating a fundamental paradigm that simplicity and complexity must co-exist to accelerate the scientific progress of large-scale systems design.