Virtual prototyping has emerged as a significant enabler for cost effective management of complex products over their lifecycle. The virtual prototypes play an important role through all life-cycle phases of products. Due to the breadth of impact, significant challenges arise in developing virtual prototypes. This paper describes the issues and tradeoffs that are important for implementing virtual prototypes. A detailed architecture is described that has been used to implement a successful virtual prototype for a complex DoD (Department of Defense) program. The paper discusses key properties of an architecture and strategies to enable its evolution over large timescales. The paper then describes the benefits of this approach.