The waterfall model of software development was formally described in 1970. It was critiqued decisively by the early 1980s. It was officially succeeded by iterative and incremental methods through the 1990s and rendered obsolete, in many professional contexts, by the Agile Manifesto of 2001.However, it is still alive and embedded in the structure of the work in many organizations, not as a named process but as an unexamined assumption. Not "we do waterfall" — nobody says that. But: "the feature goes to QA when development is done." "The sprint doesn't end until QA signs off." "We're blocked on QA." "QA found twenty bugs; we can't ship until they're resolved."