The paper "CONWIP: a pull alternative to kanban" by Professor Wally Hopp and coauthors, published in The International Journal of Production Research in 1990, presents an innovative production control method known as Constant Work-In-Process. CONWIP represents a notable advance over the well-known Kanban approach of the Toyota Production System that outperforms Kanban under a wide range of settings, is more adaptable to variability, and, unlike Kanban, is suited to environments with a large number of products. The path-breaking analysis of this paper spurred a significant stream of research into the performance of pull production systems that continues to this day. CONWIP has also become a standard part of the operations lexicon and has seen widespread application in industrial settings. Finally, CONWIP was an essential building block of the science of manufacturing that Wally and others introduced as Factory Physics in subsequent work.