Waterfall project management is a linear, sequential methodology where work flows through fixed, consecutive phases — each phase must be fully completed before the next begins. Originating from manufacturing and construction industries, it was formally described by Dr. Winston Royce in 1970 and remains widely used in predictive, plan-driven environments with stable requirements. Unlike iterative approaches, Waterfall emphasizes upfront planning, comprehensive documentation, and formal approval gates at each phase boundary, making it ideal for projects where scope, budget, and timelines are well-defined early. The methodology's hallmark challenge is its resistance to change once a phase is complete — modifications require formal change control processes and can cascade backward through completed work. Understanding Waterfall's structured milestones, dependency management, and rigorous handoff protocols is essential for delivering large-scale projects where predictability and traceability outweigh the need for flexibility.