This chapter discusses and explains the life cycle of a system. He begins by saying that “every man-made system has a life cycle, even if it is not formally defined.” This is absolutely correct and should be underlined. The life cycle stages include development, production, use and retirement. Although system engineering efforts are usually concentrated at the beginning, system engineering is still necessary throughout the life of a system. Summary The life cycle of a system consists of three aspects; the commercial aspect (business case), the budget aspect (financing) and the technical aspect (product). System engineers must balance these aspects throughout the system lifecycle. During the system life cycle, the system must proceed through a series of Decision Gates. Decision doors are sometimes reviews or milestones. Decision Gates are approval events included in the project schedule. Entry and exit criteria are defined for decision gates. Decision Gates must answer these three questions:1. Do the project deliverables still meet the business case?2. Is it convenient?3. Can it be delivered when needed? Every project has at least 2 decision channels, Authority to Proceed and Final Acceptance. There are usually many more. The life cycle of a system consists of these phases: • Exploratory research phase o Study new ideas, enabling technologies and capabilities. • Conceptual Phase o Refines and extends the studies, experiments, and engineering models pursued during the exploratory research phase. • Development Phase o Includes detailed planning, development and integration, verification and validation (IV&V) activities. • Production Phase o Produces or fabricates the system of interest. • Use phase o The system is operational. • Support Phase o Services are provided that allow the system to continue to operate.• Retirement Phase o The system is removed from operation.Lifecycle-based approachesThe manual summarizes the approaches applied to system engineering.• Plan-based approach o Traditional paradigm of requirements->design->build->test->deployment. o Strengths are predictability, stability, repeatability and high assurance. • Incremental and iterative development approach o Provides initial capability followed by subsequent deliveries. o Strengths are speed and adaptability • Lean development approach o Based on lean thinking. “Lean Thinking is a holistic paradigm that focuses on delivering maximum customer value while minimizing wasteful practices.” In Lean Thinking, waste is defined as “work that does not add value to the product or service in the eyes of the customer.” o Strengths are adding value and reducing waste. • Agile development approach o A customization process to shorten the project life cycle by performing development phases out of sequence, while balancing the risk introduced. o The strengths are flexibility and adaptability. The chapter continues by asking the question “What is best for your organization?” This question is intended to make the reader think.