Toyota's kanban: a card that signals production, turning the factory into a pull system

In the late 1940s Toyota — rebuilding after the war without the capital or floor space to stockpile parts — studied American supermarkets. Customers there take only what they need, and the shelf is restocked to match what was actually taken. Taiichi Ohno, an industrial engineer at Toyota, applied the observation to the factory: treat each process as a customer of the process before it, and let consumption, not a central plan, decide what gets made next.

'Kanban' is Japanese for signboard, and the system takes its name from the cards that ride on containers of parts. There are two kinds: a production kanban authorizes making one container of parts; a withdrawal kanban authorizes moving one container downstream. As the first item in a container is used, its card is detached, collected, and carried back upstream, where an empty card is the standing order to replenish. As long as no parts are produced or moved without a card, a true pull system holds: inventory is capped by the number of cards in circulation.

The card spread far beyond Toyota. Harvard Business Review described kanban cards as one of the system's distinctive practices, and recorded that America's big three automakers each launched initiatives to build Toyota-like production systems, with adoption reaching aerospace, consumer products, metals, and industrial goods. In lean practice the returned card became the most honest bookkeeping device on the floor: it reports exactly what was consumed, and it exposes a starving process the moment one appears.

Toyota added strict rules of use — Ohno insisted kanban only works if every rule is disciplined — and the system is so durable that the same pull logic later crossed into software, where 'Kanban (development)' became its own method and boards still run on the same card rules.