The effort to well define requirements early in a life cycle is one of the major challenges in engineering programs. Studies have shown that both technical and managerial factors influence requirements quality. However, despite the numerous requirements engineering techniques and methods, there is little knowledge of how to integrate them into a systematic requirements process that considers technical and managerial activities. In this paper, a requirements engineering and management process for concept phase of complex system life cycles is proposed. The process integrates, systematically, a set of methods and techniques of requirements engineering and project management. It was used successfully in the concept phase of a complex defense system. The business process approach is used for the process modeling. The effectiveness of the process is analyzed against a set of lean enablers recommendations to deal with unstable, unclear, and incomplete requirements in managing engineering programs. The involvement of organizations in strategic, tactical and operational levels provides acceptance and commitment of stakeholders and ensured that the requirements are defined, understood and interpreted in different contexts. The results suggest that the requirements engineering and management process allows a requirements engineering work organization: to create an effective means of planning, coordination, and stakeholder engagement; to produce requirements that meet customer needs; and to define the correct system.