Kanban

Origin. Taiichi Ohno at Toyota (1950s-1960s); the word means "signboard" or "card." Adapted to knowledge work by David Anderson (2000s).

Mechanism. Work flows through a system in response to pull signals, not push schedules. A kanban card authorizes movement of one unit of work; when a downstream station consumes an item, it sends the kanban upstream to authorize production of the next item. This creates a closed loop: work-in-progress is bounded by the number of cards in circulation, and the system self-regulates to match production to consumption.

Procedure. Define the workflow stages. Set WIP limits for each stage — the maximum number of items allowed in that stage. When an item completes a stage and moves downstream, it frees capacity to pull new work into that stage. Visualize the flow on a board. When a bottleneck occurs (work accumulates at one stage), the limit prevents upstream overproduction and makes the constraint visible. Improve the constraint; do not work around it.

Applies to. Manufacturing, software development, service delivery, any process with sequential stages and variable demand.

Limitations. WIP limits set too high provide no constraint; set too low, they starve the system. Also: kanban reveals problems but does not solve them. A team that sees work piling up at a bottleneck but does not address the bottleneck has a kanban board, not a kanban system. The discipline is in stopping to fix, not in continuing to visualize.